Plex Transcode struggles

You have a perfectly capable GPU already, the problem is that the OS is older than the CPU/GPU. Also not convinced you have all the networking smoothed out but the easier thing to do is update your kernel to support the CPU/GPU and load the right GPU driver.

Some hints here:Plex Media Server on Ubuntu 21.10 with Intel 12th Gen (Alder Lake) - #11 by Crispok1