"port is already allocated" for 443: your NAS's own web page uses 443 (Synology DSM, Unraid with SSL, TrueNAS). Publish Reelhost's 443 on another port, such as "8443:443", and forward your router's port 443 to 8443. If you don't use a web address, leave 443 out.
For 8099: change only the left number, such as "8100:8099", and open http://your-server:8100.
The page won't open: use the server's address on your home network, http://, and the port you published. docker logs reelhost shows whether it started.
Can't set the password: the first-run password can only be set from a device on your home network.
"Reelhost can't find Jellyfin's settings":/jellyfin-config must be the same folder as Jellyfin's /config, and Jellyfin must have started once.
Jellyfin isn't answering: check JELLYFIN_URL. In the compose file it's http://jellyfin:8096; when Jellyfin isn't on the same Docker network, use the server's address and Jellyfin's published port.