Many thanks for everyone's help.

So I got it working with a windows client first by using APP_BASE_URL=http://joplin.home:22300 and adding a static hostname to the hosts on my DNS server. That worked for Windows clients in the LAN.

Th iOS app would not work with that url however - when testing the connection in the app settings it just said "please wait". After many attempts I entered the url in the form http ://192.168.2.xxx:22300 and got a dialog from iOS asking if I want to permit the app to access to local network (that was not asked when the hostname was in the URL). Despite agreeing it didn´t work but I realised that the issue must have to do with local dns resolution on iOS.

Changed the APP_BASE_URL=http ://192.168.2.xxx:22300 and pointed all client to that address and it works.

Thanks again for your help