You can use either of the two "merited by me" posts.

Use static slider and any 'mempool monitoring tool' like jochen-hoenicke's to manually set a good fee rate;
or manually change the server in 'Menu->Network->Server->Pick from peers' and click "Auto-connect" to switch it off.
Make sure that Electrum is properly shutdown when you're closing it or the setting may reverse back to it's previous state
(To close normally: do not swipe out, use double back and wait for it to close by itself).

I personally haven't encountered that issue maybe because I've picked a server on my phone instead of auto-connect.

Quite, and that must be in your lightning funds' outbound capacity, not on-chain.
But you're not actually "paying" that amount, it will be sent back to your on-chain funds, you'll only pay the service fee.

The fee, it's what written in the swap window (changes depending on BTC trading price) and the on-chain transaction fee.

Unfortunately, there's no way to tell when an address was created since technically it can exist and viewed from a blockexplorer as long as it's valid.
In the Blockchain however, there is no address database whatsoever, only transactions.

Anyways, my previous post about the recovery phrase is for newer accounts.
Older blockchain.info account are way complicated to restore since the recovery phrase can't be used to recover the private keys.

What do you mean by "wallet"? Do you mean address? Because you've mentioned you can see your balance.
If so, it's not needed for recovery at all.

What you need to restore the wallet to other clients or to a new blockchain.com account is the "backup phrase" (info),
that's the 12-words that you can get from the security settings (you won't be able to get it without logging in).
If you didn't made a backup of the recovery phrase, then your only option is their customer support.

In Electrum, if you didn't selected "native segwit" prior to editing the derivation path to m/84'/0'/x', it will still create a wallet with legacy/p2sh-segwit addresses depending on what's selected.
It's worth the try.

There's a third-party feature that'll enable to to have some inbound capacity, that's the "swap" button in the 'channels' tab (View->Show Channels).
To use it, you need to wait for your channel to reconnect (open status), then input an amount in "You send x BTC" (at least 0.0002), all of the info will be updated depending on what you input,
that includes a "service fee" and on-chain transaction fee.

After using the feature, a set of transactions will be held and the amount you've input will be sent to your on-chain balance and deducted from your lightning balance.
A portion (most) of that amount will be added to your inbound capacity.

Bitcoin Core will also display a similar error if you've loaded it with a different wallet file but AFAIK, it will try to salvage it if there's enough valid data in it.

Anyways, for Bitcoin core's wallet.dat, using "salvagewallet" is still better when trying to fix a corrupted wallet.dat.
To use it, launch bitcoin-qt with -salvagewallet as an additional start parameter.

Example for Windows: create a shortcut of bitcoin-qt and add -salvagewallet to the "Target".
Then use that shortcut to use Bitcoin core with salvagewallet.

Note: After using the shortcut, there will be a backup of your wallet.dat in the same dir as your wallet.dat, but it's best to keep your own backup.

Try to copy a random xpub and paste it somewhere else, for example:
Check every characters if something changed because there may be a variant of "clipboard hijacking virus" that changes 'extended public keys' instead of addresses.

If not and you have no idea where you might have copied it, try to link both of your hardware wallets to Electrum, both Trezor (latest firmware) and Ledger should have "native segwit" option when creating a new wallet using a hardware device.

I'd suggest you to use the coin control as HCP suggested,
You can use 'SHIFT+Left Click' to select multiple coins (UTXO) at a time, you can make 2 transactions each using half of your available coins.

Or pay 1.2sat/B, it's higher than 1sat/B but not as expensive as 2sat/B  
It's possible by editing the 'absolute fee' above the fee slider next to the equal sign of the 'Target fee' and 'bytes' in the advanced preview.

AFAIK, it contains a mini private key format.
If so, this post from 'stack exchange' may be the one you're looking for if you are planning to sell the bitcoins in an Exchange:
Re: How can one redeem a Casascius Physical Bitcoin?
The linked reply has every information and the links you need.

-typo-

Is the other PC's Electrum connected after you restored the Seed phrase?
The connection icon below should be a green circle.
Because if it's newly installed, there may be a delay before it can display the wallet's balance.
Or if the version is too low, it will not connect to the network at all.

You can also check the address tab (View->Show Addresses) if your address is listed there.

Good, it says "ok", then the BIP39 seed is valid.
Next is to match the derivation path to your addresses, do they start with '3' or 'bc1'? After inputting the seed phrase, there'll be a "Script type and Derivation path" window.
On that screen, select "native segwit (p2wpkh)" if your addresses start with 'bc1', select 'p2sh-segwit (p2wpkh-p2sh)" if they start with '3'.

If it's legacy (starts with '1') and Electrum is connected (green connection icon), then the seed phrase is just from an empty wallet, could be from a wallet with unique derivation path or other issues.

Try clicking the option under the box where you input the seed phrase, then tick "BIP39 seed".
After pressing 'ok', if it says "BIP39 (checksum: ok)", your seed is a valid BIP39 mnemonic phrase and you may continue.

If "BIP39 (checksum: failed)", there's something wrong with the seed phrase and you'll likely need to provide some info like the Electrum version when it was created and other non-private stuffs.

Blocks are still valid even without any transactions in it aside from the coinbase transaction.

Look, the genesis block nor the next block doesn't contain any additional transactions: btc/block/0 and btc/block/1
Here's the block where the transaction that you're talking about is: btc/block/170

No one can tell which is which exactly that's why there is no reliable list.
Some of the old block's reward could be an early adapter's bitcoins not Satoshi's.

No for the second part; if you open the .psbt file using a text editor, it will just assume that the contents are any of the text character encodings and will display non-readable data.

I guess that it's a binary encoding: https://github.com/bitcoin/bips/blob/master/bip-0174.mediawiki#Encoding
But the encoded data is the same whatever option you've used to export the partial raw transaction.

If he use "Copy to clipboard", it will result with a Base64 string; IDK for the "Export to file" but it looks like a 'binary version' like he said.

@77Network Either (1) use the "copy to clipboard" and paste it on a text file then you can use Bitcoin Core (even offline) to decode it using the command: decodepsbt.
Or (2) Sign it first (then the exported file/text back to the online machine will be in HEX) and before you broadcast, you can decode it using your usual tools.

Of course, all of this are after the upgrade.

This is the correct Github repository of Electrum: https://github.com/spesmilo/electrum
Sorry to say that you're funds were hacked and bitcoin transactions are irreversible.

For those who've posted late and planning to post: the issue is already solved.
The OP said it in this reply:

O...kay.. If it worked just recently then I assume that your wallets have saved the latest transactions.
So just do "HCP's export tutorial" link in my post and import the WIF (base58) private keys of addresses with balance to Bitcoin Core
(if the "standard client" is what you mean by "regular client").

You can also share the armorylog.txt from the datadir so the developer could see the actual issue.

Is Armory working (just acting up)? Then the best solution is to simply send the funds to Bitcoin Core through a transaction.

Next option is to Import the private keys to Bitcoin core through core's console/command line using importprivkey (how to use).
You can get the address' private keys in Armory's "Wallet Properties->Backup This Wallet->See other Backup Options".
Here's an 'export from Armory' guide with pictures by HCP: https://bitcointalk.org/index.php?topic=4746784.msg43255691#msg43255691