If you can find a way how ffmpeg (a.k.a the Plex Transcoder) can use hardware transcoding, while Plex is running as a service, you’ll be a hero!
Plex can run as a scheduled task, it can also run as a service. Several approaches have been developed and used.
I am running it as a service, but I cannot use hardware transcoding for it. (restricted user account, utilizing nssm.exe)
Others are using the task scheduler, which usually allows hardware transcoding.