For snaps this was fixed already some time ago:
You can try the suggested solution of adding the additional helper line to udev rules to make them like these:
# Nitrokey FIDO2
SUBSYSTEM=="hidraw", KERNEL=="hidraw*", ATTRS{idVendor}=="20a0", ATTRS{idProduct}=="42b1", TAG+="snap_chromium_chromium"
TAG=="snap_chromium_chromium", RUN+="/usr/lib/snapd/snap-device-helper $env{ACTION} snap_chromium_chromium $devpath $major:$minor"
And I can see the rule for Nitrokey FIDO2 in snap config too:
@simon Can you check that further?