Well it is no longer a separate fork build, there may still be issues bugs it is an extra option you have to enable under the advanced transcoder settings if you have compatible hardware.
It uses VA API https://en.wikipedia.org/wiki/Video_Acceleration_API , testing has forcuse don Intel quick sync since intel origonated the API but a number of other cards / CPUs support the API under windows / linux
Something to check out if you have been maxing out your CPU on your Plex server.
There are still issues with image quality / blockiness on linux servers unfortunately, depending on your configuration.
Official support info.
https://support.plex.tv/hc/en-us/articles/115002178853-Using-Hardware-Accelerated-Streaming
Blog: https://www.plex.tv/blog/smooth-stream-operator/
Word of warning the HW encoder is very blocky at times on Linux using Intel Quick sync