Is each movie in their own folder? How are the files named? I'm assuming when you say that you tried adding the subfolder you mean that you add "Movies/DC/" to the library config.
Jellyfin 10.10.3 (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)