I haven't tested this on Zorin specifically, but it worked for me on Fedora Workstation which also uses gnome and gnome Software.
First, get the current order of preference:
gsettings get org.gnome.software packaging-format-preference
Using the "Try Zorin" option of the ISO, the output is ['flatpak:flathub', 'flatpak', 'deb', 'snap'].
Then rearrange the output and plug it back in using set, probably something like:
gsettings set org.gnome.software packaging-format-preference "['deb', 'flatpak:flathub', 'flatpak', 'snap']"
This won't affect the apt command, though, and I'm not even sure if it will bypass Canonical's scummy and fraudulent fake apt installers that just silently trick you into using their garbage snaps when you had explicitly asked for the native release in the Software store. They're already intentionally, wilfully, and maliciously circumventing user choice with apt so I would be shocked if they aren't also doing it in gnome Software somehow.