Is it safe now to keep OS up to date all the time? Ubuntu 20.04 LTS, right? We can keep that updated, just don't upgrade to other release?
Yes, that's exactly what John just said. In fact, you even quoted him..
The base system will still be 20.04, and you should only do apt update/upgrade...do NOT do a full dist upgrade if the OS prompts you to upgrade to 22.04.
(emphasis mine)This means you can keep packages and OS updated, as long as you stay on 20.04 LTS. It has support until 2025 as far as I know, so no real need to upgrade Debian to 22.x or higher until then.