I faced the same problem - Clearing the Android Jellyfin App Data solved the problem. My guess is, the app for some reason caches the resolved ip address of my.domain.tld, so clearing the Jellyfin App Cache is probably enough.
I'm on Android 14 (no Lineage OS), Jellyfin App downloaded from Google Play.
THANK YOU SO MUCH! Man, I've been troubleshooting this issue for an entire day. I was checking my cloudflare certificates, nginx proxy manager options, proxmox settings, and NOTHING was doing anything. And it didn't make sense, everyone was how it should be, and it was working in browser and other places, just not on the Android app. This was all it was... I even checked this thread at some point, but didn't read up to the end until now. Thanks!