That’s exactly the same case as Windows. The built-in photo/video players don’t support them out of the box, but do if you install the free codec from the store, or you can install any 3rd party players you like.

There are lots of great things about Linux, but out of the box support for licensed video codecs isn’t magically better than Windows

How many distros support h264/265 out of the box? They probably don’t support most HEIC images either since they’re HEVC on the inside

Yes, exactly. The github readme has been pretty confusing, especially since the project changed names and there are still some references to the old name. But it was already usable as a runner in Lutris before launch and works much better for me than 8-26 which is pretty out of date now! I play a lot of non-Steam games.