Just had a quick google around, unfortunately it looks like the short answer is "not without a PC", for now at least.
I think it would take the developers of Roblox to release a version for a headset like the Oculus Quest 2, so it doesn't have to run via a PC and can run natively on the Quest. If there is any kind of workaround possible to use without a PC, I'd imagine it'd be a right ball-ache.
