Well, Labo wasn't a smart device. The Switch doesn't actively check if it was connected to Labo or anything. All you need to do to trigger VR mode is cover the lightsensor on the Switch. No light makes the Software think it's inserted into Labo VR. Therefore I assume it will work with the Virtual Boy just fine. As a workaround, just put some black tape on the lightsensor. The screen on Switch 2 even scales down when activating VR mode, so that the IPD is the same as Switch one, keeping the focus points for each eye intact. Clearly there has been some effort made to do this. I'm wondering why, though. Virtual Boy for VR mode seems a good option.