I literally just finished doing this over the weekend. I went with fedora since I find it more stable and easier to use than the other distros plasma bigscreen works on. There have been a few bugs when using a controller but other than that it works great! I highly recommend it.

OSMC: https://osmc.tv/

My suggestion would be KDE Neon or Fedora KDE, since both are straightforward and have official Plasma Bigscreen packages

I don't think atomic distros like Bazzite are a good fit for something like this since Plasma Bigscreen does not appear to have an official flatpak. It can be done but there are some drawbacks.

If you go with one of my suggestions, you will want to install multimedia codecs that do not come with the OS by default.

Here is a guide that will work on KDE Neon.

This guide is for Fedora.

Unless you are just trying to use up hardware you already have laying around, do not do this. The experience is extremely suboptimal and much more expensive than just buying a better streaming box.

If you have not spent money yet there is still time to avoid this mistake.