I am on Fabric 1.21.1
modloader 0.16.12
Fabric API 0.115.4
Journeymap 6.0.0-beta.43
Mapfrontiers 2.6.0p2

Everything is the same version server side as client side
I can make frontiers fine, but global frontiers does not seem to work for me. When I join a single player world F8 is also not doing anything. I have deOP and OP'd myself on my server to try if it works again.

This is my code for the Modpack on curseforge: i7f62KKt

Server side there is also Carpet and CarpetExtra, which are not in the modpack.

It's very strange that F8 doesn't do anything; it seems like a different issue than not being able to create global frontiers.
Please try the latest beta (1.21.5-2.7.0-beta.9); it also requires updating the dependencies (Fabric API, JourneyMap, and Forge Config API Port).