@nikolal thank you for your help! I'm trying to connect to my home-server (a small raspi) via public-key authentication but: step-by-step. I don't even know YET how to configure it in a secure way :)
It's always the same: you don't know anything, you are frustrated, you try it, again and again, it works... or it doesn't... you are frustrated... but then it works (somehow!)