My Plex server runs on an Asustor NAS (Celeron N3050 based) and is still very busy with the sonic analysis. At a rate of approx 10 albums per hour it will take until autumn for me to use this featureIf you have an old Intel PC / MacMini and run plex on that it actually does sonic analysis of the tracks and will suggesting similar albums and similar tracks to the ones you are playing and some of the suggested playlists are autogenerated from sonic similar tracks. The reason this isn't available when deploying the plex server on a RPI is they use some Intel GPU architecture (for transcoding movie content on the fly) and this sonic analysis tries to re-use the same GPU.
I have 2 Plex servers for this reason - one mainly for Movies / TV shows / LiveTV / Audiobooks (happily running on a RPI) and one dedicated to Music on a small intel linux PC.
But besides that - for serving music Plex uses almost no ressources at all ... especially when compared with roon.