With a simple hub it Just Works, there is no need to attach the hub as device and a mouse or USB attached to it, work just as they would if you connect them to your laptop.
However with a higher end hub, designed for your monitor, power and everything to be run though it, it just does nothing. Qubes ignores it entirely aside from it working to power the device.
What needs to be done so everything works?
If you’re not clear what type of USB Hub I’m referring to, say the CalDigit Element Hub. It’s designed so you just connect the hub via Thunderbolt to your laptop and nothing else. Everything else just gets plugged into the hub.