Resizable BAR is only required for gaming performance, and having it off does not affect video transcode in any noticeable way.
Before Plex broke ARC compatibility (they’ve repeatedly said they never supported it in the first place, but it did work before) it had no problem transcoding as many 4k streams with HDR tonemapping inside a Ubuntu VM on Proxmox, on which GPU passthrough requires you to disable resizable BAR.
Here is a link to my testing with it, and there are others who had it working as well:
But at this point, Plex supporting it officially (to prevent a version release from breaking it) is the actual issue. It can currently transcode but not do HDR tonemapping in hardware.
