Ok. it was the solution. The wallet has been restored!
Good for you!
I still don’t understand what’s wrong with the Electrum installation on this computer...
I can't telll you what happened, all I know is most of what you wrote didn't make sense.
Better to uninstall it and always use another machine for electum.
Just in case, I'd wipe the system and reinstall from a fresh Linux download.
Whats the best way? Using tails for Electrum by default?
Tails is mostly designed for privacy, but the pre-installed Electrum makes it convenient for this purpose. Depending on how much value you're storing, you may or may not want to look for a more secure setup (such as a Trezor hardware wallet). If it's $200, I wouldn't worry about keeping it in a hot wallet. But if it's a lot more, I'd change my setup.
Also: considering you may have entered your seed phrase in a wallet that may have been compromised, it wouldn't hurt to create a fresh Electrum wallet, securely backup your new seed phrase, and transfer your funds there.
Before doing that, read
How to lose your Bitcoins with CTRL-C CTRL-V so you don't just trust CTRL-V
