The USB device applet that lets you attach a USB device to a VM doesn’t have my webcam listed in it. On regular Linux distro, it works fine.
I have no USB qube.
You need to have USB qube to be able to attach USB devices to other qubes.
What if I installed Qubes on an external USB drive? Can I have USB qube without breaking it?
Only if you have more than one PCI USB controller. Then you can leave the USB controller to which you’ve connected your USB drive in dom0 and use other USB controllers for sys-usb.