I’m facing the same issue. Did you ever manage to resolve it?
Edit: I have just found the solution on Reddit:
I got it working similarly. I did not have to enable https or Magic DNS.
For my situation I was trying to use plexamp.
In Plex, I have remote access set to: “Not available outside your network”
Then under Settings>network
there is a “Custon server access URLs” field
I put my tailscale ip address for my plex server there. “https://:32400”
Example: “https://your-ip–:32400”
After that I could connect using plexamp to listen to my music from my phone. Whether on wifi or cell
Here is what the manual says about this field:
Custom server access URLs
A comma-separated list of URLs (either HTTP or HTTPS), which will be published to plex .tv for server discovery. This can be very useful in a few cases: if you’re using a VPN to get back home, if you’re using a reverse proxy in front of the media server, or if your networking configuration is otherwise unique. For instance, if you have your own custom domain with subdomain, you might add:
https://plex.–mycustomdomain.com:32400
Hope this helps someboby.
similar to what aakoss said, but spelled out exactly what I did.