It would be great if there were logs in the electrum, in which you could see from which application the transaction was made or any data about the device. but as I understand it is impossible.
I think you misunderstand how Bitcoin works. The transaction was in all likelihood, not sent from your device.
Once someone has your seed or private key(s), they can simply clone it into a wallet on their own device (pc/mobile) and then have full access to your funds. The most likely explanation is that someone has access to your seed.
However, the difficult part for anyone to figure out is
how that person got access to your seed... usually, the answer is, like you say, because of fake apps or people storing seeds digitally (screenshots, emails etc)... but according to you, none of that is true in this case.
In that case, you would need to sit down and think of everything that has happened since you installed the wallet and started using it to try and find the hole in your security. There isn't really a lot else that other people can do for you at this stage