Hiya! If you check a game listed in the Oculus store, you'll see which platform the game supports. Sometimes, a game will support both Quest 2 and Rift S (the PC version of a game), but many games will only support one or the other.
If you want to let us know which game you're having issues with, we can provide more clarification! Here's a photo with where you can see which platform the game supports:
Oh, gotcha! That would be because Beat Saber isn't on our list of cross-buy compatible games. The Rift/Rift S is our other headset platform specifically for PCVR use, so naturally, it has its own Rift library. Cross-buy compatible games are games that are only bought once, but are offered on both the Quest and Rift library for the user. Since Beat Saber isn't on that list of cross-buy compatible games, you would need to re-purchase it on the Rift library to use it in PCVR.
Hope this helps!