It should be under “Settings>Transcoder.”
There is a point “Activate HEVC video transcoding” where you can select to use it always or only for HEVC source files via the dropdown.
Hope this helps! 
Hardware transcoding in PMS 1.43.1 is not working for some Arrow Lake CPUs.
See Hardware/GPU/Quicksync transcoding broken on Beta 1.43.1.10540.
If it was working on an earlier release, you may need to fall back until Plex gets the kinks worked out.
Also, Plex is looking for people to help with testing. If interested, see https://forums.plex.tv/t/hardware-gpu-quicksync-transcoding-broken-on-beta-1-43-1-10540/937145/112.
Oh, okay, so leaving it the way it was working wasn’t an option? I’m happy to help—here’s the big tip: do it the way you did before; that’s how it worked!
Thanks for the Info bro…
No, unfortunately that doesn’t work either. It’s no big deal; I’ll just wait until it works again…
Have you tried the forum preview linked here?
It’s a preview of 1.43.2.x and has confirmed fixes for Arrow Lake-based iGPUs.
Not yet, bro. I didn’t know they were already working on it. Now I’ve gotten all worked up for nothing 
… How bad can you feel? Me: Yeah! … Plex is running on a Proxmox LXC for me—please correct me if I’m wrong. First, I’ll back up the entire LXC, then I’ll switch Plex to beta… Then I’ll run “curl -LsSf https://repo.plex.tv/scripts/setupRepo.sh | bash” because “apt update && apt upgrade” doesn’t work yet, and then I’ll test it… If it’s okay, I’ll let you know; if it’s not okay, I’ll let you know too and restore my backup… If it works, I’ll let you know; if not, I’ll let you know anyway, and I can just restore my LXC backup and everything will be just like it is now?
At least we’ll know the outcome of your test I guess 
The repos don’t work for betas or forum previews, so you’ll need to manually install the appropriate release from the link above.
