You can disable transcoding, but then your users may not be able play some videos on some of their particular devices. MKV is just a container. The codec of the video, audio, and subtitles are what matter.
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)