Qubes 4.1 - Network-Manager VPN connection setup

Ok, I managed it.

As a solution that everyone can follow easily:

Mullvad VPN setup on Qubes OS 4.1, based on Debian:

Additional step / preparation before you start with Micahflee’s vpn guide:
Launch a Terminal in your Debian Template (Template: debian-11) and run:

user@debian-11:~$ sudo apt install network-manager-openvpn-gnome -y

reboot your Qubes.

crosslink: PSA: using a VPN under Qubes for Dummies - #5 by Sven