md5sums have to read the entire file before calculating the checksum. I'm not sure how long you waited, but it could be several minutes for multi-gigabyte movies.
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