Yet another dude with Jellyfin Android app not connecting when using domains

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Could you provide your Jellyfin log via pastebin or privatebin? I hear a couple different setups here and it's a little confusing, i.e., using both RP and Wireguard. I also don't see anything about certs, but that doesn't mean much. You could try http://mydomain.tld, could double-check whether remote connections are allowed to the server for the user account you're attempting to use, but without looking at a log those are shots in the dark.