I’m not going to say using a different distro will fix all your problems but yeah, your experience is not normal. A lot of this is because Ubuntu is not highly recommended. It’s just popular, but there are a bunch of terrible decisions it makes that barely anybody recommends it.
Of course Ubuntu just threw out the old installer for debian files, and didn’t replace it yet. Wouldn’t want a user to just be able to easily install files!
Checks out. Ubuntu is also one of the only modern distros that doesn’t come with Flatpak, which is a massive store of applications that’s quite easy to use and has a huge store of applications.
May I recommend something like PopOS instead? It’s based on Ubuntu so everything from there will work on it, including .deb files. It’s basically Ubuntu but with way, WAY saner defaults and a better beginner experience. I think your experience will be a lot better on a nicer distro.