KDE Connect open up firewall ports

I do not use iptables.
Here is my solution depends on your preferences (UFW or FIREWALLD).

Firewall Configuration Guide

UFW (Uncomplicated Firewall)

If UFW is active, it’s necessary to allow the required ports:

sudo ufw allow 1716:1764/udp

FIREWALLD

Allowing Ports for TCP

To allow TCP ports:

sudo firewall-cmd --zone=public --add-port=1714-1764/tcp --permanent

Allowing Ports for UDP

To allow UDP ports:

sudo firewall-cmd --zone=public --add-port=1714-1764/udp --permanent

Reload Firewalld

To apply the changes, reload the firewalld:

sudo firewall-cmd --reload