It’s open source and not for sale

You could just use SDL. Very easy to integrate into a C project. BUT SDL doesn’t come with any UI primitives so you will need to make buttons, sliders etc yourself.

This is a phase that most Linux enthusiasts go through at some point. It takes time to understand what a distro really is.

People see distros as being much more different than they really are because of the default settings between distros being so different from each other.

At the end of the day a distro is basically just a way of choosing which group of people you want to trust to package software for you.

You can always just use the version you have and run an update after it’s installed.