we can not call something that has happened only one time a "cycle". it was a one time thing that it took bitcoin 4 year to get on full rallying mode and end up with a similar big bubble at the end that also popped similarly to last time.
if you look past the previous time (before 2013) you can see that there has not been any cycles. all we had was a series of events from 2013 to 2018 which had some similarities but a lot of differences too. this is what you call "cycle" which is wrong.

it is not possible to send coins to an address by simple accidents such as entering an address character wrong. so there is a good chance that what you have received is a payment or a donation. you also have no way of contacting the sender although you can always search the transaction ID on a block explorer and see where the coins came from then reverse search the address in a search engine and see if that turns anything up (eg. it could be the address on a profile of someone on this forum).

important thing to remember: if some day someone contacted you claiming it was a mistake and asked you to send the coins back and you wanted to do it, first ask them to sign a message from the address that sent you the coins to prove that they are who they claim they are.

it depends on how you define terms such as "strong" versus "fragile". if the only factor you consider is the price the the answer to your question is simply no. it is because the bitcoin market is still pretty small and the order books are not yet as packed as they should (for a lot of reasons). that means the price remains very volatile and at times susceptible to manipulation.

but if the factor you consider are the factors that make bitcoin what it really is which is a decentralized currency then the answer is obviously yes. nothing can change the fact that bitcoin is completely secure, decentralized, global, censorship resistant, fast payment system without a middle man.

it doesn't make any difference to provide the PGP signature of the file itself or provide hash of the file and then PGP signature of the hash. i don't yet know why some projects do it but they do it nonetheless. for instance Ubuntu does exactly this. under Linux both of these steps take only two steps to write a small line in terminal so it is not that big a deal.

besides under the hood things are happening the same way! for example when you are verifying PGP signature you first compute hash of the file then check the signature versus that. so hashing is still a part of it.

the only size limit is the block size, in other words you can inject a garbage data a little less than 1 MB in one transaction's output to the bitcoin blockchain. 20 byte (which is actually 40+OP_RETURN+push-byte size) is the standard rule that the bitcoin nodes are enforcing to reduce the chances of abuse. there is also transaction fees that will prevent such shenanigans to some extent.

the thing is that bitcoin is a payment system so it's "ledger" should only have to store payment data not arbitrary messages hence the "The best practice is don't."

unfortunately some banks have been scamming people like this for a long time now and there is not much we can do about it, this is more severe in certain countries that don't have clear rules about bitcoin otherwise you won't see something like that in a country like Japan where bitcoin is a legal currency.
this is also the main reason why so many people have put their trust in an extremely high risk centralized and shady altcoin called tether.

that's the thing though, not only nothing has changed about coronavirus but also the situation has gotten worse. back when price dropped about 2000 new infected people were found every day and the death rate has been very small but now there are 75000 new cases are found every day with death rate a lot higher than before. so you can't really say we are moving away from Corona!
what happens is that the manipulation and FUD is fading away so price is going back to where it should have been.

halving on its own is only a short term hype that has never been able to cause a small price rise for a short amount of time before the correction hits. the real rise is always due to adoption and mainly occurs after the halving when the real effects of 50% smaller daily new coins is felt by the entire market accompanied by an increasing demand.
right now as the big manipulated dump is coming to a conclusion and the whales accumulation is near the end we are seeing price go back to above the intrinsic value and get out of the undervalued state. this could kick start the rally although the fear could still be a preventing force.

you are putting a lot of faith in pure chance with no reason. that's the recipe for disaster when you are trading because what you are doing looks more like gambling rather than trading. such swings may not even happen or worse happen at very different prices like going to $8.5k then down to $7.5 which means if you sell at $7.1 you lose a lot of money.
you are also making another huge mistake: buying altcoin. specially when you say you buy it when bitcoin drops. everyone knows that whenever bitcoin drops altcoin drop harder.

bitcoin has never had any correlations with any other market specially stock market ever and it didn't start to have any now either. if anything bitcoin is correlated to the global fear which was the only reason why bitcoin price dropped in the first place.
also if there were any correlations bitcoin should have continue falling like stocks all through march instead of reversing and going in the opposite direction (up) unlike stocks.

after block number 227,835 all blocks must include the block height in their coinbase transaction. they do it by including the number in their only input's signature script. if you are unfamiliar with transaction structure and scripts read [1] and [2].
numbers exist as bytes inside a script and bytes should be pushed to the stack with the appropriate push OP code. this push must be the first pushed item and the rest can be anything.
example from last block: https://blockchair.com/bitcoin/transaction/02d8cdb103f50532e2f18d9d1f85c016468ee0294908d387e38f80b99410d893
signature script is:
decoding this script is like this:
03 -> push following 3 bytes
348809 -> in little endian = 624692
041f... -> the rest can be anything

[1] https://bitcoin.org/en/developer-reference#transactions
[2] https://en.bitcoin.it/wiki/Script

you should be warned that that if you reveal your redeem script or public key then anybody can claim your bcash coins for themselves because the "nested SegWit" or the P2SH-P2WPKH scripts are simply the hash of the following redeem script: OP_0 <20 bytes>. since bcash doesn't have SegWit it evaluates this redeem script as a simple push of data which always evaluates to true and doesn't need any signature.
so all they have to know is the 20 byte hash or the public key to hash and then claim the coins as their own.

it has always been about two things with Binance: making as much money as possible and having as much centralized power in the scene as they can.
right now they are fully controlling the altcoin market as they have kicked almost all altcoin exchange competition out of the scene. they won't stop there, entering mining scene will also give them a lot more power specially if they start mining altcoins and could get a big enough pool to control the altcoins that way too. it won't cost them much either since it is just a pool not a mining farm needing as much electricity.

there are a lot of other things that are taking a lot more lives than Covid-19. for instance car accidents are killing or disabling about 50 million people each year or about 10 million people die from cancer every year. if you start putting your life on pause just because some pandemic is spreading, you have to keep your life on pause all your life!

you should report such scam videos to Youtube so that they can remove them from their platform. as they have been doing it already with a large number of scam videos using a wide variety of schemes to rob people of their bitcoins.

it is possible because ethereum is also a copy of bitcoin so most things that matter are exactly the same as bitcoin. and the site is using private keys (not even public keys) so they have the chance to build it from the base up (private key > public key > hash > address)
the hash is the different step and is the stupidest method too, instead of using a hash algorithm that returns a 20 byte result (like RIPEMD160) it uses Keccak-256 hash of the uncompressed public key then drops 12 bytes of it! the remaining bytes are the address.

uhhh so that's why there have been an increased number of requests for a "large amount of testnet bitcoins" lately all around the internet. i even saw some testnet faucets that i used for some of my tests go dry recently. i always knew there must be something like this involved.

i don't think that is possible, or at least it would be extremely difficult to exclude all the LN stuff and release a secure and working new version with other features. the problem is that they have been making commits to the master branch which is the main branch that holds the current state of the project. if it were another branch then it may have been possible to pull other features to master and make a release but not now.

i don't think it is an algorithm they use to remove videos from their platform. it is mainly based on reports a video receives plus the topic/contents of that video. for example when someone is advertising an ICO scam or spreading wrong market analysis to mislead people into buying a pumping shitcoin and is reported, the video is going to be removed.
the "good content" even if reported, won't be removed because there is nothing wrong with them.

i call it reverse bubble bursts, some may even refer to it as dead cat bounce but i won't call it "relief rallying"
besides the timings don't match. bitcoin reached the bottom in a massive sell off on March 13 and reversed back up in 3 days and has been creeping upwards ever since (80% up). while stocks continued falling during March and have only recently started seeing some small reversals.

i disagree with saying "BTC also fell much, much further", that is just wrong. you are simply ignoring the volatility factor of bitcoin and the fact that a 40-50% drop although scary is not uncommon in bitcoin market but the same size dump in any other market is extremely rare. for example the ~60% drop in crude oil price that you mentioned here is simply outrageous.
i said this in another topic, when you want to compare drops you must put them on a same scale. a 40% drop in stock market is 80% drop in bitcoin, a 60% drop in crude oil is 90% drop in bitcoin. something like that. but if bitcoin dropped smaller or even the same it means bitcoin outperformed all of the other assets.

as for the effects, i still say COVID-19 never had anything to do with bitcoin and it is not the virus pandemic that has caused the drop but the fear and manipulation.