The problem is that in 10.9 tags were added to search. In 10.8 only titles and people, etc., were searched. So searching is much more resource intensive in 10.9.
Jellyfin 10.10.1 (Docker)
Ubuntu 24.04 LTS
Intel i3 12100
Intel Arc A380
OS drive - SK Hynix P41 1TB
Storage
3x WD Red Pro 6TB CMR in RAIDZ1 (JF Library)