Oh no, that's our *Secret Asian Technique* to keep the moisture at bay :D

But I believe he already contacted someone (hopefully a trusted professional) to recover the drive as a response to LoyceV's suggestion.

It's hard to give a safe answer to that since 15 years is too long to speculate, but:
So far, Electrum is doing a great job with its "backwards compatibility" after these years.
Versions before the new seed version system (Electrum <2.0 - older than Oct 2015~2012) can still be imported to today's latest version (v4.1.5) and can restore exactly the same wallet.
With exception to the oldest releases (v0.34 & older) with patched bugs and changes in the key derivation system.

Yes, the backup of the wallet files are enough but make sure that the backups are made after you've encrypted the wallet files.
That's because it'll generate a new "hdseed" after encrypting the wallet, making the old backups obsolete.

Windows has an option to hide/show the file extension but since it says "Type: 21 file", it means that the extension isn't ".dat" which shouldn't be the case with "File->Backup Wallet".
You can display the extension in Windows in the 'file explorer' menu "View->File Name Extensions".

Yes, 1 wallet = 1 backup with ".dat" extension.
You can set a name when you use "File->Backup wallet" but make sure that the correct wallet is selected in the "Wallet:" drop-down menu at the right,
you can also set a wallet name during wallet creation (in the later versions). IMO, naming those differently is enough to tell them apart from each other.

How about the other two options?

If all are empty, then there's really an error in your backup.
Recovering the wallet file from the laptop is your best option which has a great chance, as long as the "tea" hadn't penetrated the HDD/SSD.

Electrum developers wont be able to "directly" help you in recovering your seed phrase since it isn't stored to any server.
You'll likely get the same advice as these.

Have you tried to restore the seed phrase with BIP39 option enabled? That will enable you to click "next", then select one of the options (start with the middle).
Users usually use that to create Electrum wallet with P2WPKH-P2SH (P2SH-SegWit) addresses.

It will only be unclickable if the seed isn't correct.
Try to replace some words with similar ones from the wordlist that could be mistyped when recording the backup. Some of them are similar.
An easy way to do this is to type the first three characters of the word during the restore process in Electrum and check the possible words from the selection.

You can also try to restore it with "BIP39 seed" enabled in the option and make three different wallets, each with one of the three available derivation paths.

You can add these links to your research, the latter may be the answer to the former:

• support.ledger.com/hc/en-us/articles/360015739499-Sign-or-derivation-path-is-unusual
  Quote
  However, users of third-party wallets such as Electrum might also see this warning
  message even if the public key or signature request comes from a legitimate wallet.
  This is due to the fact that these wallets use an incorrect derivation path, which can also be valid for Bitcoin.
• https://github.com/spesmilo/electrum/blob/master/electrum/base_wizard.py#L417-L419
  
  Quote
  # There is no general standard for HD multisig.
  # For legacy, this is partially compatible with BIP45; assumes index=0
  # For segwit, a custom path is used, as there is no standard at all.
  Those are comments, the actual code is below it.

It depends on the type of Electrum wallet where you're importing private keys.
If you're importing to an existing wallet, you'll only be able to import to an "[Imported]" wallet, any other wallet will only have "sweep".

If into a new wallet, the "import bitcoin addresses or private keys" option in the new wallet wizard should work for private keys.

The instructions are in the first page - first post.
If your wallet is not in the list, try to find a similar feature in your wallet, usually, it's named as "sign message".

If there's none, you can import the private key of the address to one of the wallets in the OP with "sign message" and "import private key" feature.
Then sign a message using it.

On the contrary, some clients are referring "Unspent Transaction Outputs" as "Coins".
Example: Electrum has the wallet's available UTXO in the GUI displayed as "Coins" tab (View->Show Coins).

I think it's fine as a non-technical term for UTXO.

I don't know if you're being sarcastic to the OP because it's related... so sorry in advance if yes:

Your keys are also outside of the curve, three out of four in your list are spent because those are within the first valid private keys from 0x01 which can easily be "hacked":

• 0000000000000000000000000000000000000000000000000000000000000000 - 0x3f17f1962B36e491b30A40b2405849e597Ba5FB5 (unspent - invalid prvKey)
• 0000000000000000000000000000000000000000000000000000000000000001 - 0x7E5F4552091A69125d5DfCb7b8C2659029395Bdf (spent)
• 0000000000000000000000000000000000000000000000000000000000000002 - 0x2B5AD5c4795c026514f8317c7a215E218DcCD6cF (spent)
• 000000000000000000000000000000000000000000000000000000000000000e - 0x5A83529ff76Ac5723A87008c4D9B436AD4CA7d28 (spent)

All but 0x3f17f1962B36e491b30A40b2405849e597Ba5FB5 have a valid prvKey so those are spent.

I think it's because the swap service provider (swap server) can only accept 0.002tBTC per swap:

• https://github.com/spesmilo/electrum/blob/master/electrum/submarine_swaps.py#L462
  
  

BTW, Boltz have a testnet swap but unfortunately, I haven't successfully sent lightning tBTC to it yet using channel connected to "endurance" (Electrum 'trampoline' channel for testnet).

• testnet.boltz.exchange | Select LN-BTC -> Bitcoin

With that, even Dave wont accept the job;
You can try to bruteforce it yourself but I'll tell you that the odds of getting the correct password with random/sequential characters is extremely low even if you have a super computer.
It's important that you at least know some possible words/characters in the password.

Important Note: please do not entertain any PMs that offering "help" who'll ask for your wallet.dat file, there are lots of scammers doing that.
Stop buying wallet.dat files!

Uhhhh... Why are you asking me?
OP haven't responded with detailed information in any of his topics (I take it with a grain of salt), that's why I asked.

BTW, not only the speed, he's accepting Lightning Funds so, his channels should have enormous amount of inbound capacity which isn't easy to accomplish.
If he responded, an answer that "connects" will clear any qualms about his story.

Do you have any idea of what the password might be?
If no, forget it, it's not possible to "bruteforce" it with random characters or words unless it only consists of very small number of characters.

If yes, and you don't have the resources to bruteforce like GPU or a fast CPU,
you should consider contacting Dave:

• Profile: walletrecoveryservices
• Thread: Bitcoin Wallet Recovery Services - for forgotten wallet password

Tails supports printer, you can print the QR code if it's for someone near you.
Alternatively, you can take a picture of the invoice/address's QR using your phone's camera.

If showing the QR code is the actual issue: you can display it using the small "QR icon" beside the "copy icon".

How many characters is that presumed private key?

As said above, "Wallet Import Format" (WIF) Private keys which what Electrum supports doesn't start with '1'.
It could be a ECDSA Private key depending on the number of characters, that only requires some formatting.
But do not share it to anyone including me.

That's good, for you and the community.
Also, that was exceptionally fast, only took about 5 hours after you've asked the question in 'Beginners and Help' board, about 4 hours after the first reply.

How did you implemented "lightning network" in your store by the way?

From what article is it? (I mean, the quoted part of your previous post)
Google search with the quote only returns with article for "Trading" and it may be talking about cryptocurrency in general, not Bitcoin specifically.

Read these instead of random internet articles:

• en.bitcoin.it/wiki/Mining | en.bitcoin.it/wiki/Mining#Reward
• learnmeabitcoin.com/technical/mining

It is fine to say that.
New coins aren't pre-generated or reserved, Bitcoin isn't like tokens with defined total amount.

Bitcoin's 21million supply isn't because there's already 21m bitcoins in reserve (it's not a hard-cap either).
But it's based from the calculated "block rewards" from the first block, to successive "halving" until it reach 0.

github.com/bitcoin/bitcoin/blob/master/src/validation.cpp#L1068-L1078
<Link edited to highlight the correct lines>