Super short answer - officially supported distros and their officially supported desktop environments.
Longer answer: Why these two? Because we have two entities we have a long standing partnerships with that have been amazing to work with. As we grow, we will be adding additional distros that also have shown themselves to be amazingly cooperative.
Understand though, we have folks who are rocking Nix, Qubes, Debian (with newer kernels in play) and other distros here all over the forums.
Arch for example, has shown its community is very willing and able to provide amazing community support. This is coming to the Linux Landing page here very soon (like in the next page refresh). In 2024 and beyond, we will be looking at distros that align with where believe we can forge amazing community partnerships.