Some people may say that "Being able to spend the fund without any need to that particular wallet means that it's decentralized". Even if the wallet is open-source, this is not necessarily true. 
To me, being decentralized means that you can run the wallet from the source code and make transaction with that particular wallet without relying on a third party and a centralized server.

For example, trustwallet gives you a seed phrase which can be used for recovering all your private keys.
If trustwallet doesn't exist a day, you can import your seed phrase into another wallet and access your fund. This doesn't mean trustwallet is decentralized. Because whenever you use trustwallet, you have to connect to a centralized server. The server you connect to can know your IP address and hurt your privacy. As trustwallet is close-source, it's also possible that they have access to all your keys and are technically able to move all your fund even without your permission.


I would categorize the wallets into the following types.

1. Custodial: You give a third party full access to your fund and lose your own control. Example: Coinbase

2. Close-source, Centralized and non-custodial: You have control over your fund, but there is no guarantee that you are the only one who has access to the keys. There's also a centralized server which can hurt your privacy. Example: Trustwallet, blockchain.com

3. Open-source, Centralized and non-custodial: (Provided that the code has been reviewed) You are the only one who has full control over the fund, but you still connect to a centralized server which is not good for your privacy. Example: Mycelium

4. Open-source - Decentralized and non-custodial: (Provided that the code has been reviewed) You are the only one who has full control over the fund, there is no third party involved and you can protect your privacy. You can run the wallet without any need to a third party and a centralized server. Example:  Electrum (if you run your own server) and bitcoin core.

In this case, you are the maker because you make the order and someone will take the order.

Note that in every trade, there's one maker and one taker.
Maker is the one who creates the order and waits until it's filled by someone.
Taker is the one who fills the order created by a maker.

What do you mean by putting an unmined block on the blockchain?
Do you mean you have found a block and now you want to broadcast it to the network?

What's the point of broadcasting blocks that have been mined before?
It's not that you can mine a block now and broadcast it at any time you want.
The block reward goes to the miner who solves the proof of work problem faster than others. So, your block won't be accepted by other nodes and there will be no reward for you.

You can't use your 2FA wallet as a co-signer for your multi-signature wallet.
Electrum 2FA wallet is a multi-signature wallet itself. It's actually a 2 of 3 multi-signature wallet in which the user and trustedcoin sign the transactions.
Also, the seed phrase you have for your 2FA wallet doesn't work in the same way as your other seed phrase. The seed phrase created for a 2FA electrum wallet is a backup for 2 master private keys and 3 master public keys.

How did you import the address into your wallet?
Did you use its private key or you imported the address itself?

If you imported the address and you didn't import the private key, now you have a watch-only address and that's why you can't make any transaction.
If you imported the private key, it can be due to a bug in blockchain.com wallet. Their wallet is so buggy and I wouldn't be surprised if that's the case.

Anyways, if you have the private key of the imported address, you can import it into another wallet like electrum and make your transaction.
Note that if you have already imported its private key into blockchain.com wallet, you should be able to export it.

I changed my signature and left the campaign too.
Thank you Best_Change for the opportunity you gave me. It was an honor to participate in this campaign.

As far as I know, old users had a "wallet.aes.json" file which could be used for recovering all the private keys.


The other important change is that, they give users a BIP39 seed phrase which can be used for recovering the wallet without any need to their service.


Are you sure that you receive the emails from blockchain.com and they are not phishing emails?
I also have a wallet on blockchain.com. But I never receive email from them.

I won't make any deposit, because I'm not sure I will be able to make withdrawal without verifying my identity.
I remember they officially announced that KYC is mandatory for all users. So, even if it's shown that I have a withdrawal limit of 2000 dollars per day, it's still possible that they don't process my withdrawal until I verify my identity. They have full control over users fund and can do anything they want.

There isn't really any difference.
A bitcoin private key provides 128 bits of entropy and there is no way to increase the security of your private key to more than 128 bits.

Let's say your seed phrase is compromised and the hacker needs to brute-force your passphrase to access your fund.
Whether you use space between the words or not, the entropy provided by your passphrase would be more than 128 bits. Even if the hacker knows that you have used a seed phrase generated by electrum as your passphrase, the entropy would be 132 bits which is still bigger than the entropy provided by a private key.

Yesterday, it was confirmed that Trezor users email addresses has been breached. For more information, read the topic created by Pmalek.
Trezor mailing list breached
   

Trustwallet is close-source. I recommend you to use separate wallets for each of your coins. For example, for bitcoin you can use electrum.

There was no BIP39 seed phrase in the wallets created before the upgrade they did in 2016. But users had full control over their fund.
As far as I know, in the old wallets, users had a json file which could be used for recovering all private keys if they knew the encryption password.

Again, I am not saying blockchcain.com wallet is secure. It's possible that they have access to the keys. It's also a buggy wallet with an unresponsive support.

Blockchain.com is a non-custodial wallet and exchange.
Their wallet gives you the seed phrase and you have full control over your fund. Of course, I wouldn't recommend anyone to use blockchain.com. It's close source and we don't know whether the keys are stored on their server or not.

You are right. I just tested it with a fresh electrum wallet and it worked. I remember it was not possible to import a wallet generated by electrum into bluewallet if there was no used address in the wallet.
Something has probably changed in the latest versions of bluewallet.


That may be because electrum doesn't support IOS.

Bluewallet use BIP39 standard for generating a seed phrase. But it can be used for recovering a wallet using the seed phrase generated by electrum as well.
There's just a requirement. The wallet must have been funded. If there is no used address in the wallet generated by electrum, you can't import it into bluewallet.

Right.
The seed phrase is derived from a random number through some mathematical calculations in your device and there is no need to internet connection for that.


Right.
All your private keys can be derived from your seed phrase and that's all you need to recover your fund.

They can also force many of non-custodial wallets to stop their service. Most of non-custodial wallets are connected to centralized servers and can shut down at any time.
For example, trustwallet is a non-custodial wallet. But there is no guarantee that it will work the next time you want to make a transaction.
As stated by pooya87, if you want a wallet which you can be sure that it will always work, you can use bitcoin core. It's open source and no centralized server is involved.

With generating the seed phrase offline (assuming the old iPhone is clean and there is no malware in it), you can increase your security, but you don't really increase your privacy.

When it comes to your privacy in electrum, there is no difference between a wallet including private keys and a watch-only wallet. In both cases, you connect to a server to get data.
The server you connect to can know all the addresses belong to the same person and also link them with your IP.

Go to "Addresses" tab and use one of the addresses shown there. All those addresses are yours. If you don't see "Addresses" tab, click on "View" at top of window and select "Show addresses".
You can also go to "Receive" tab and click on "New address" button. In this way electrum will show an address at right side of the window. That's one of addresses shown in "Addresses" tab.

Warning:
Before sending bitcoin to your wallet, make sure you have downloaded electrum from its official website and you have the seed phrase (a series of 12 words) in a secure place.
Also, double check the address after copy-pasting that. There's a malware changing addresses to hackers addresses.

In the case they want to charge extra fee, they have to add an extra output to your transaction. I haven't ever made any transaction using their wallet, but I don't think they do so.
The only fee you pay when using their non-custodial wallet is the fee you pay to miners.


Now, they know your IP address and can link it with your addresses, your previous transactions and your balance.
As their wallet is close-source and we don't know what is happening behind the scene, it's also possible that your seed phrase has been stored in their server. With having your seed phrase, they can know all your private keys, public keys and addresses.


It's still better to use electrum. Recommend them to use electrum and avoid any close-source wallet, especially coinbase.

I've logged in to my account a few times since they forced users to verify their identity. I used a VPN from a European country at all times.


I just made a search and found an announcement they have made in December, 2021.
Binance to Update the Denomination of Withdrawal Limit from BTC to BUSD

According to the announcement, the unit of measurement is no longer BTC. The withdrawal limit is now measured in BUSD.