Some info I wrote for another user, pasting it here:
The big drawback is oculus does not allow devs to access passthrough, so I can't show you a transparent overlay or anything. This might change eventually, and I'll implement immediately.
Right now, the setup is something you only need to do once, but it's a slow, careful process. My advice would be to start small, setup a single room or two connected rooms, and you can add on to a larger space later once you find a good anchor setup.
So, how do you actually map? Well, nose gap is what I find easiest. Don't be super precise, pull your walls in a bit tighter than the real ones. Walk the perimeter and hit the main corners, and then use large cubes to block over sections of objects (rather than many small cubes to mark individual chairs, just mark the whole chairs/table as a big cube)
If nose gap is not cool, you can try doing it 'blind' (rest the quest on top of your head , but above your eyes) and mark corners (you'll feel vibrations for each click)
I guess you can also enable the handy "double tap for passthrough" feature in the settings, but it might not activate if guardian is off.. I gotta test.
I admit, it's a pain. Especially for those who have large playspaces. But it's worth it, even having a rough setup with an anchor, you'll be able to use the rest of the app and can fine-tune things later on.