In the same kind of guide about using flatpak in templates, I wrote one explaining how to use snap in templates
https://dataswamp.org/~solene/2024-10-16-snap-on-qubesos.html
This is different than https://www.qubes-os.org/doc/how-to-install-software/#installing-snap-packages explaining how to install snap in a template to allow AppVM to persistently install snaps in their own storage.