I confirm that plasma-firewall thinks ufw is disabled although I verified it is enabled using systemctl status ufw.
When I try to “enable” the firewall using plasma-firewall in the System Settings GUI I get an error:
Error enabling firewall: An error occurred in command 'setStatus':
How to fix `plasma-firewall` error in System Settings GUI when running `ufw`
Open /usr/lib/kde_ufw_plugin_helper.py and change the first line from #!/usr/bin/python3.11 to #!/usr/bin/python3.12. This fixed the issue for me immediately and makes sense since Manjaro is currently on Python 3.12.