You PC could have been infected with malware via downloading and insta some random apps. Which operating system have you been using?
Did you download the electrum app from the official source and even verify the signature?
Its a Win10 machine, the wallet (as portable version) was downloaded from the orignal website and I used it for years without any problems. My wallet was also passwort protected which is why I am asking myself if malware just waits till the wallet has been opened.
Dont get me wrong, there is nothing I can do now but I dont want to make the same mistake twice. So I want to know how that was possible and if this could be a real scenario. i had the wallet since 2017.