I love these little machines. Personally I plan to use my mini PC as a media PC for me and my significant others TV when I move in.
Also, if you run servers that are configured using a web UI(this is a super niche use case) small and low power PC's like this are awesome to use as terminals/controllers. It's super niche and even I can admit there's not a ton of reasons to do it that way, but I've done it before and especially for specific network setups it can be super awesome.
Plex/Jellyfin setups are also good use cases since they require very little computing power.
This is unrelated... How did you get yourself to be a Linux pro? I am trying to switch, but I am hopelessly Windows-minded.
Also, yes you're making it more complicated than you need to. Go to the steam website and install, or use Ubuntu's app store. That's how I've gotten it before, I prefer getting it from Steam's website.