Does the kcm_firewall support firewalld? It doesn’t seem to be working for me (doesn’t show that it’s running, nor does “enabling” the firewall do anything). If I click the about button at the bottom (after a password prompt) it does display firewalld as the backend, and firewalld is the firewall that I am using.
With all the password prompts I’m presented with, it feels like this could be a group / permissions issue.
I do not see how plasma-firewall could be functional wiith firewalld backend as it does not support zones, nor service based rules. With plasma-firewall you can only manually create rules based on ports and only for all connections.
For instance, if you want to enable kdeconnect you would have to manually set rule for required ports range while in firewalld you would just have to enable kdeconnect service.
Depending of what your are doing with Firewalld, you can be prompted twice somehow.