H266 isn't really well supported on client devices. I was encoding my library for a while with H265, but have moved on to using AV1 for my library since most of my devices can play it directly.
Jellyfin 10.10.6 (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