@ryanpage On Ubuntu 24.04, in Gnome, go to 'Settings → Apps → Vivaldi' and enable 'Access Hardware Information' and 'Read/write access to U2F devices exposed'. For 22.04 you should be able to change these permissions from the Snap App Store app.
Alternatively from the terminal you can issue the following (tripple-click to select the entire line):
sudo snap connect vivaldi:hardware-observe && sudo snap connect vivaldi:u2f-devices
The reason you need to do this manually is that apps cannot automatically connect to these without a special exception from Canonical/Ubuntu, which we have now requested
https://forum.snapcraft.io/t/request-for-automatic-connection-for-u2f-devices-for-vivaldi-snap/43907