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 10.10.0 (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)