Yes

Public ports : 443 only
Internal port : 22300

Yes

Yes

I suggest you try to replace "server.local" by the IP address (10.11.12.13) both in your docker compose file, and in your Joplin Client Sync settings. I already noticed that Joplin Server is very sensitive to this info (it should be exactly the same in both places), and I wonder if it's may be your problem.

Good luck,

Bruno