How do you know the server is worker fine? How are you accessing it to know that?
E:
Do you have a firewall running on your mint installation? If so have you allowed the ports (8096/8097)
Can you access the web client on the Mint installation http://:8096
Can you use that same address on your phone / another computer to access it?
FYI If you’re using 127.0.0.1 that will not work on your phone or any client that’s not running the Jellyfin server.
When you use the Jellyfin app which server address are you putting in?