I think it's a question of how sharp the tool is, and how 'idiot-proof' it's been made. Ubuntu is as idiot-proof as Linuxes go, but the more knowledgeable you get the more you find use for a sharper tool that fits your domain requirements better.

Debian is molded to the server domain pretty closely; Red Hat / Rocky is ideal in regulatory environments; Alpine when the priority is to be lightweight and reliable; I run Void on my personal machines because it's the most BSD of the Linuxes and stays out of my way when I need to do weird stuff.

If you're a beginner, you can append 'ubuntu' to your google searches instead of 'linux' and get an answer that makes sense. You'll know when to move on from ubuntu when you have to search 'foo bar linux' to get a usable answer.

Personally I think debian is the best server OS to learn. It's sufficiently similar to ubuntu that you can get away with either one really, they aren't very different as ubuntu is based on debian.

Not OP, but ubuntu is among the best documented an supported, which is critical for beginners.

What may not be good about Ubuntu for some is that it's too bloated and not difficult to learn for someone who wants to hang their hat on that.

Moving from Ubuntu to another Debian installation, including debian is no big deal.

Nix?