Use the "Check Node" button under 'Join the network'.
Your IP Address should be automatically detected but if not, manually type it along with the correct port.

AFAIK, there's none.

You can use the command suggested by hosseinimr93 to import a private key or importaddress to include its associated transaction(s) to the wallet.
If you're planning to use this method and there's more than one address to be imported,
I'd suggest to use "false" 'rescan' flag for the first few (so it wont scan right away) and "true" on the last.

Bitcoin Core has RPC commands: createrawtransaction to manually create a transaction and converttopsbt to convert it into PSBT.
Neither require the UTXO set nor blockchain to use.

Reference: developer.bitcoin.org/reference/rpc/index.html

Thanks, I previously edited it from "4 vMB" because I decided to use "Weight Unit" instead but forgot to add "million".

Blocks can be lower than the "maximum" block size (currently 4 million Weight Units).
Most of the first thousands blocks are empty and the rest (until Bitcoin became famous) only have a small number of transactions included,
so their size are only a few kB.

For example: Block #1000 doesn't have any transaction in it aside from the coinbase txn; its size is only 0.216 kB.

Is this about Electrum's 2FA?
Because I can't find any topic about 2fa wallet with a seed phrase in your post history and you didn't tell from which 2fa wallet is this about.

If it's Electrum: the 2fa is there to protect the "wallet file", which is in a PC/Phone, which is an online vulnerable environment.
The wallet file doesn't contain the seed phrase or your second master prvKey so it's useless on its own without the 2fa authenticator if accessed by hackers with the correct password.
In this case, a non-2fa electrum wallet would have been hacked already.

The seed on the other hand is air-gap, in a safe offline environment, so the only way to compromise it is to have physical access to it.

Again, you have answered neither of the users' questions because saying "you found 1 or 4 address" doesn't make sense unless you specify how you found them.

But anyways, there is a way to test and try if your seed phrase is invalid for having a wrong character and to find if it has a balance:
You can import it to Electrum by toggling "BIP39 seed" in the option during the restore process.
It will show "BIP39 Checksum: ok" below the seed if it's valid (with very small error margin).

Then in the next window, clicking "Detect Existing Accounts" will prompt Electrum to check the mostly used derivation paths if any of them are funded,
it will display a list if there's more than one funded 'account'.

But take note that it's only for Bitcoin not Altcoins.

This part looks convincing, I'll settle with "average" then.
But I can't help but think that there should be a factor to consider when discarding half of the list so I'll do my research on "chance" in general.

Thank you.

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@notphus Pardon for the going quite off-topic; that was just about the small chance of your seed phrase's "good checksum" to be false-positive.

Okay, and all of those count in the 1/16 chance because it's only based from the last 4-bit, including the non "gravity" ones.
So actual chance to get a valid seed phrase when "scrambling the 12 words" will be a lot lower than 1/16 since most of those "other words" aren't in any of the 12 words to be scrambled.

Well, the tricky part is while the checksum is only the last 4-bits, the last word is influenced by the last few words because each word is equals to 11-bits.
I'm thinking that while it's true that the checksum last 4-bit "0000" has 1/16 chance, some of those valid mnemonic phrase's last word can't be "gravity" because there other words that end with "0000".
That's why in that scenario where the words are scrambled, we should be computing the chance based from the number of words or at least it can't be 1/16 chance.

Note: 816 - 'gravity' is actually "01100110000".

Yes, always 1/16 if we're talking about the 4-bit checksum and the entropy, it's simply because a random 4-bit can only have 2^4 combinations.

But:
In which case, we can't use the entropy to compute the chance.
And I doubt that the chance is constant for every 12 word seed phrase since the each 12-word combinations can have lower or higher chances than the others.
So it's hard to give an accurate rate, but I doubt it's still as high as 1/16 in this case.

BTW, we're not helping in solving OP's case 

Yes, you wont be able to create another account if the previous one is unfunded.
support.ledger.com/hc/en-us/articles/4404389482641-Add-your-accounts?

The question is for us to find out if he should be restoring the seed with derivation path account level higher than 0,
the "4 addresses" may be from his first or next accounts.

His previous response "found 4 addresses" doesn't make sense as a reply to my previous post so I guess that the seed phrase doesn't have issue;
but he never answered that last question yet.

True but isn't that 'average' only for situations when all the words are candidates for the checksum?
If the only candidates are his 12 words, then the odds should be way lower than that (depending on the words), or wont even form another combination with a valid checksum.

That's because it's not designed to look for every possible "accounts" but only pre-specified derivation paths listed in:
https://github.com/spesmilo/electrum/blob/master/electrum/bip39_wallet_formats.json

Since the seed phrase is obviously not made by Electrum (it's a BIP39 seed),
it's most likely from another wallet with unique derivation path that aren't listed in the '.json' file above; or just a random seed you've taken note of.

He mentioned that the "checksum passes" so the words must be in the correct order.

I prefer "for information" conversations public so other users can use it for reference and also to minimize duplicated topics.

No, but blocks aren't something you can pre-generate then put in the blockchain days later.

It's called "block" + "chain" for a reason,
because the next block should be built on top of the latest block since the previous block's "hashPrevBlock" should be included to the next block's block header (so on, so forth); that connects the chain.
If you somehow managed to build a valid block now, but haven't broadcast it right away, then it wont be valid after its height was occupied by another miner's block.
Not to mention, the validity of the transactions in it.

BTW, you should specify the steps that you've done to build a block.

Then you would have to pay miners with amount greater than the reward that they usually receive from their mined blocks.
You're basically asking a miner to mine "your block" which is technically theirs since they will do the proof-of-work.

Here are the miners: http://bitcointalk.org/index.php?board=14.0 | Go to "pool" sub-board.

Abdussamad's reply will work if you've selected "keystore 1" or "keystore 2".
If it's 'keystore 1', there's a shortcut to get the master private key, it is by using the 'console' tab (View->Show Console),
then type: getmasterprivate()

It can get ugly if you somehow selected "keystore 3" which is owned by TrustedCoin.
In which case, requires manually contacting them to co-sign your transaction.

Okay, so there's no missing character in the seed phrase since you already found 4 addresses.
So, the actual issue is finding the correct "derivation path" of the funded address(es).

Because there can't be a typo if you can properly restore the seed phrase with BIP39-supported wallets (it has a checksum).

Question is, how many Bitcoin accounts did you have in your Ledger Live?
Because aside from the first, every consecutive accounts can't be recovered by using the default derivation path (it needs tweaking).

With that, your initial concern persists because in events of a theft, if the USB flash Drive/PC is stolen, then your wallet files will be stolen as well.

If you still want that, Tails has the option to create a "persistent storage" where you can store the wallet file.
It's basically an encrypted storage in the USB flash drive which is exempted from Tail's "amnesia". It's protected by your admin password.
My suggestion is at least set a different password (strong ones) for the persistent storage and your Electrum.

I can't find any PR that added any "taproot upgrade" wallet command or GUI feature, it's only added by default for newly created descriptor wallets.

For now, you can manually import a new tr() parent descriptor for it to be able to create Bech32m addresses.
The steps are similar to this post: bitcoin.stackexchange.com/questions/108006/how-to-make-a-taproot-transaction-with-bitcoin-cli
But instead of xpub, use xprv.

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That version is still in development so it's still open for updates.
Try to open a new issue - feature request: something like "add an option to create taproot descriptor for old descriptor wallets".