I installed opera on linux mint 20 xfce with a deb file I downloaded from here, the official site. As I had problem playing videos I uninstalled and I removed the authentication key on Software sources. After one day the key comes back! I tried with terminal commands apt-key delete but the key again comes back after one day!
It's the same issue described here https://forums.linuxmint.com/viewtopic.php?f=47&t=262031
What files-settings opera installs and where? This is not normal! How can I fix it?