Mirrors are extremely useful for checking your avatar toggles/poses, FBT calibration, whether your feet are touching the ground or if you're crouching/floating, etc. They should never be completely forbidden.

Solutions like making them visible to others or culling players work better, as others have pointed out.

Instead of attempting to disable this it, it might be easier to just fix issues with these. For example, using a camera or mirror to see through walls is only useful because the far clipping in those is very high. Maybe the world could override this and set it so you can't see players reflected in mirrors if they are more than a meter away, and possibly the same for cameras.

Having this be an option that can be enabled and disabled via Udon, would allow players to use them when a game is not in progress maybe or when spectating. But this depends on the game in question, so best to just leave it up to the world creator.

Make it a simple "game world" preset, then it should be easy for world creators to add to their worlds, rather than have them adjust weird clipping distance numbers on their own.

I would like Udon to be able to toggle this. Example: ForceHidePersonalMirror(true). Hides the personal mirror if it's deployed. And then you can show it again, back in the same spot.

This could be fixed by the world creator using a shader that only displays in the mirror (_VRChatMirrorMode == 1) that covers up anything too far away, but it would be better to have it as a built-in setting for world creators, also as someone else stated, it is still possible to do this with cameras on avatars, allowing players on PC to still cheat in these worlds, also the camera can be used to cheat in the same way

If only cheating in game worlds was the problem... The main concern is privacy and security, VRChat shouldn't provide any tools that could help malicious people to get an unfair advantage like cheating in games, spying through walls, etc...

These designs should have been thought before the personal mirror was implemented, if it creates problems that does help people to go against their TOS, the personal mirror should be removed until a better solution is found.

We're interested in exploring adding this and other options as world rules creators can opt in for their worlds.

We don't have an ETA for that feature just yet, as a lot of design has to go into it -- but it is in the pipeline.

Rather than going "hey I want to kill this entirely", I think it would be more productive to disable the part of this that actually spoils the experience... like, say, the toggle for remote players.

World authors should be able to disable the Environment and Remote player settings on the portable mirror. I don't see a good reason to disable the entire mirror function itself.

You can do the exact same thing with your camera and also with shaders etc on your Avatar. The only thing they could do is maybe adding a small Mirror Indicator (Just like for the Camera), but that should be something you can turn of if you don't want indicator flying around everywhere.