Linux definitely has HDR. I've been using Bazzite with Steam Big Picture mode as my TV interface for years and can use HDR just fine.

I definitely recommend piracy, but there are also ways to get streaming services to send full quality streams. I won't recommend them though, because you shouldn't have to do it in the first place for a service you're paying for. Just pirate and use a media server or something like Kodi for a nice interface for local files.