That issue (not Librem specific) from my experience is linked to sys-usb not having enough memory assigned by default. Reserve 500mb in settings to see the issue disappear, and reduce slowly until sweet spot is found.
If you inspect sys-usb dmesg logs, you should see errors linked to memory issues in dmesg. Oomkiller most probably. If i recall well, something linked to usb proxy gets killed and results in the device disappearing under camera used qube.
If I recall well, 450mb is a better default for sys-usb having an onboard camera.
If it works for you, please open an issue on github. Something in the lines of augmenting sys-usb default memory when a camera is detected at install would be a nice feature/bug correction for our new remote working era we now live in. 
Edit: the more sys-usb template enabled at boot services consumes ram, the more sys-usb reserved ram should be increased. I confirm that behavior since 3.2 and always shipped sys-usb with more reserved ram then the defaults, and confirm that sys-usb based on fedora-35 consumes a tad more ram then whatever Fedora template version it was on Qubes 3.2. Damn Fedora release cycle is annoying.