In the Jellyscrub plugin, did you convert your existing BIFs to trickplays? The plugin should prompt you to do that when you go to the settings for Jellyscrub.
Jellyfin 10.10.7 (Docker)
Ubuntu 24.04.2 LTS w/HWE
Intel i3 12100
Intel Arc A380
OS drive - SK Hynix P41 1TB
Storage
4x WD Red Pro 6TB CMR in RAIDZ1