I will perform the write up and submit to Engineering about checking for free space.
Given a lot of distros go for a small root partition (some as small as 30GB now), and the default for Plex is in that root partition (established when the space was much larger by default and libraries weren’t massive as they are now), if one knows they have a large library, why not take the prudent step an just move it out of the root to a place where it has room?
Plex doesn’t know how your system is partitioned (I don’t look).
The installer doesn’t mandate where the APPLICATION_SUPPORT_DIR goes but I guess I could put it in /home/plexmediaserver (although that creates a logistics & support nightmare) if the root filesystem is under 128 GB allocated.
In the interim while we all figure this out and have time to ingest the results, may I offer:
