The ArchiCADWiki articles on setting up for remote access note that you may have to edit your local hosts file so that within the office you can use the FQDN just as when you are outside of the office. (Of course, if you use a VPN, you do not need a FQDN, hosts, etc in any case.)
Setting things up takes careful reading of the documents - one missed step is all it takes for things not to work locally or remotely. Once set up, you're good to go and won't have to fiddle with things anymore.
Cheers,
Karl
AC 28 USA and earlier • macOS Sequoia 15.3, MacBook Pro M2 Max 12CPU/30GPU cores, 32GB
One of the forum moderators