Sorry for your loss.

This is a common subject here often these days (like this https://bitcointalk.org/index.php?topic=5161786.0), about paper wallet security.
Most of people think it is easy and simple to make a paper wallet, but it is not.

Generating a paper wallet is risky. You shouldn't have put your computer back online afterwards... In my opinion, the best is to invest in a hardware wallet, which is safer BECAUSE it is easier to use.

I believe the attacker got your private keys few days after you put your computer back online. He was probably monitoring your address, waiting for you to put more money there.