For PCVR games, it’s exactly the same as normal PC piracy. You can add them as non-steam games and then tick the “show in VR library” option so they actually appear in the VR shit.
For standalone, on the Quest 3 (which, BTW, can also do PCVR), there is an app called Rookie Sideloader that can pull (nearly) anything from the official store without paying for it and then it’s just installed as an unknown app instead of showing up in the default app list.