The wallet profile was missing on the PC, as well as the passphrase to restore it. I don't think it's my PC.
It is unclear which profile is missing from your PC. Can you specify? Do you have any idea how this occurred?
This fact itself tells us that your computer is very likely infected with some malware.
I believe that the actions were carried out on a third-party resource. Does Electrum have tech support to check this? How can I communicate them?
Electrum is a self-custody wallet, meaning that you are the only one who possesses your private keys, and there is no third-party resource that could cause you to lose your coins. However, if you have saved your seed phrase to an external source, that was a major security failure on your part.