Yeah, this space seems pretty sparse. Some of the Radxa SBCs are getting closer to a hardware solution for your vision, but there isn't real mainstream software. A self-hosted DNLA server is probably the most realistic option but DNLA has seemed to fall by the wayside in favor of paid streaming and plex/jellyfin.
That said, Tailscale did not exist when DNLA was popular, and DNLA over Tailscale seems a really promising non-jellyfin avenue.
Ultimately the problem will be lack of hardware decoders and poor interop with Dolby, DTS, etc.
https://bret.dk/radxa-dragon-q8b-a-laptop-cosplaying-as-an-s...
I think the problem is that legit apps like Netflix are super restrictive about what they'll run on. Even if you just do it through a browser you need to be using Chrome on Windows or whatever or they'll restrict you to 720p.