You said it yourself — you’re new to self hosting, and CasaOS fits what you want to host. As a starting point for getting rid of hosted services, go with that for a start.
Sure, you won’t immediately be getting your hands dirty mucking about with dockers and stuff, but you will have your working home server. For learning and experimentation, I second @Scipitie@lemmy.dbzer0.com’s plan B — use another machine to test building the same setup on a base Linux system.
If you’re like me you probably have an old laptop lying around that wouldn’t be great as an always up, day to day server, but as a testing environment to mess around with docker containers it should be fine?

Yeah, “Ubuntu wants you to use their new feature” is… unsurprising. Explaining the benefits and purpose of that feature? Now you’re talking.