You can import the "descriptor" or "master private key" to Sparrow but you can't export a seed phrase from it.
Also, it's not possible to create a seed phrase from existing master private key, the steps in seed generation from 'seed phrase' to 'seed' to create the Master PrvKey is irreversible.

Can you show us the source of that info?
Because depending on the procedure, you might get away with just individual private keys or others.

Should be in your internal storage (not root), inside a folder named "org.electrum.electrum".
There'll be no notification but an in-app message near the center of Electrum saying "Backup saved" followed by the backup directory.

Okay, the third sentence is still applicable to the question regardless of its relation to the puzzle.

As explained by others, there are more private keys than addresses but the possible collisions aren't grouped in a specific range,
address derived from a prvKey in 160-bit range could have a collision within the same range so we can't just excempt prvKeys from 161~256-bit in the search.
And addresses don't have a "range" or any indicator from which private key it's derived from.

Try VanitySearch, Vanitygen may be too outdated for your new generation RTX Nvidia GPU.

VanitySearch Bitcointalk Thread: https://bitcointalk.org/index.php?topic=5112311.0
VanitySearch GitHub Repository: https://github.com/JeanLucPons/VanitySearch

Because the creator of the puzzle said so plus the consistencies in the solved puzzle ranges.
Because there's no way to verify that the unsolved puzzles' keys are really within that range, so it's not guaranteed by any data or math.
We only got the addresses (and some public keys) and as you know it, we can't guess the private key's range based from those information alone.

For reference, here's the puzzle creator's post: http://bitcointalk.org/index.php?topic=1306983.msg18765941#msg18765941

For reference: doing so will return with a different error which is noted with the supported maximum "storage version" of the used Electrum Client version.
It's the "seed version" that's recorded in the wallet file.

He's using "myNode" (introduction) which has a built-in Electrum server which should work out of the box when enabled.
Given that Sparrow and Blue wallets work without issue (through Electrum server option), there must be something in his Electrum client that's causing the issue.

Those videos must have been created a year ago when the "Overview" and "Server" tabs are separate.
In the latest version, the server tab is merged with the overview tab.

It shouldn't be the cause of the issue though.

So, router and node seem to be configured correctly; also, enabling UPnP usually works after restarting the node.
I'm guessing that it may have something to do with your ISP.

Check your "debug.log" file if there's any entry that hints of inbound connection attempts.
It's in the data directory, open it as text.

Yes, that'll only be necessary if you're connecting through Tor.

Probably similar to Ledger's usual error where it shows twice bitcoin amount, something fixable by rescanning the blockchain.
In Trezor Suite, follow this guide (take note of your settings so you can change them back): trezor.io/support/a/discovery-error-issue

Do you have any entries in your bitcoin.conf file or the GUI's settings?
If there are, please show them (remove the sensitive parts like RPC credentials).

Have you restarted the router and PC after setting port forwarding and static IP?
Depending on the router, it may require a restart.

That's because the wallets' versions don't match, the error is self-explanatory.
You can import an older wallet file to a newer Electrum client but not to an older Electrum client.

You're using either of the versions 4.0.2 up to 4.07 in your Desktop while using the latest in Android.
(based from the "storage version" in the error)

To be more precise: Those packages are the target of typo-squatting which mark them as the "attacked packages" and not included to the new attack.

It's a good thing that you've included a link to the article in OP because the ambiguity in the post may cause some misunderstanding (already did?).

It's only possible to add a private key to a wallet with seed in the old versions.
IIRC, it's around v2.7 or close (2016), so if your wallet is that old and you did imported a private key to your wallet, then it's not covered by your seed phrase.
You can only restore it by importing its private key or get from the actual wallet file where it's imported.

For reference, old Electrum will show you this warning when you try to import a private key to an HD wallet:

No, cosigners will only sign the transaction to finalize it, there's no fee involve in signing transactions.
The fee is set while creating the unsigned raw transaction from the difference of the inputs' and outputs' amounts.

Electrum's MultiSig setup is using the same Electrum seed as its standard wallets so you can use it.
It doesn't have a specific MultiSig 'reserved number'; only "Standard" (via console), "SegWit" or "2FA".

I have a feeling that we're in an "XY Problem" situation here.
Please elaborate.

In the "Channels" tab, do you have any other channel beside those two?
If so and if it's offline or similar, it may be the listed "Not Available" balance.

While "Add Cosigner 2" window is open, you can still launch another instance of Electrum where you can start creating Cosigner2.
After getting to that part where it shows you the master public key, paste that to the "Add Cosigner 2" window.
In the other instance's next window, paste Cosigner1's master public key.

For learning purposes, that makes sense.
For real-world usage, it defeats the purpose of MultiSig.

Do not waste your time recovering it from the corrupted files.
You old password will not help you recover the current password, that is unless you made a backup of the wallet file before the password has changed.

I did some rough estimation to give you a "reasonable range" like I suggested and the result is you can only search up to 5.
With a token of %1,5in; you'll exhaust that within 2 weeks at that speed.
%1,6in will take about 2 years, more will be impossible.
The bottom-line is, using random character search for the whole password wont work for long passwords.

As I previously mentioned, it's pointless unless you can remember a good portion of your password.

If the input is the address, all you have to do is to decode it with base58 and then get the last 4 Bytes.

Address: 1H5aq8vssj9fCKdw2mYEn8enzpUMEBsUZ7
Decoded: 00b05fea8c3768f8fbb48f9c778bb36b91334cf7a169e65f22
Last 4 Bytes: 69e65f22 (which is the correct checksum)