When you go to the https URL, can you inspect the certificate the browser received and check that it is valid and that it includes your subdomain and not just domain.tld?
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)