Currently, desktop players can hold TAB to move their mouse around the screen freely, rather than having it control where they're looking in the game.

However, it would be nice if creators could toggle this functionality for certain games where it would make sense. For example, one might want to make some sort of 2D game board that would make more sense for a desktop player to interact with as a Canvas UI, rather than using traditional Unity UI inputs or VRCPickups (the latter being especially relevant given how tedious rotating VRCPickups is on desktop).

If you're worried about this being used maliciously, or about users being confused about it, you could even implement a setup like RequestFreeMouseMovement(), OnFreeMouseMoveAccepted(), OnFreeMouseMoveDenied() that asks the player for permission to enable the feature whenever a world would need it. But I can't imagine this ever being an issue, since the VRChat menu renders over everything AND can be interacted with even when this feature is in use.