The /etc/chromium/policies/managed denials aren’t the problem (though @oSoMoN, it would be great if those were made snap-specific. If you feel they should be added to browser-support, let’s discuss that in another forum topic).
The “/run/udev/data/c203:*” denials should be noise. The nividia drivers use major 195, not 203. I’ll update the browser interface for this. If you want to be sure that this is just noise, you can add to /var/lib/snapd/apparmor/profiles/snap.chromium.chromium:
Then load it into the kernel with: sudo apparmor_parser -r /var/lib/snapd/apparmor/profiles/snap.chromium.chromium
Then try again and report back. I’ll be adjusting the browser-support interface for this regardless.