So a bit of exciting news. In a different thread, @ChuckPa posted a dev-test build (NOT OFFICIAL) of plex for linux that includes an updated intel media driver:
I can confirm that this build correctly recognizes and hardware transcodes on my Intel A770 GPU!! Note, that because I also have a Intel iGPU on the cpu, I had to manually specify HardwareDevicePath="/dev/dri/renderD129" in Preferences.xml for it to use it over the CPU, but once I did that it works without issue.
