Creating a working template is a huge work. If you don’t really see how this work, I’m afraid this means you don’t have the necessary knowledge and skills at the moment.
Maybe using opensuse leap in a distrobox environment inside a regular debian or fedora template could be a possible solution for you? GitHub - 89luca89/distrobox: Use any linux distribution inside your terminal. Enable both backward and forward compatibility with software and freedom to use whatever distribution you’re more comfortable with. Mirror available at: https://gitlab.com/89luca89/distrobox
Distrobox will make my disk infinitely heavy and nix will be no happy
The user JTY wrote in qubes-devel thread:
“We have already made our own Qubes system based on OpenSUSE 15.3 for both dom0 and templateVM…”
Maybe you could ping him.
Or ask @fepitre
I have advocated for openSUSE templates quite a while ago: