Any mixed reality app on Quest can now disable the annoying VR-centric safety boundary.
Boundary, formerly called Guardian, is certainly useful in virtual reality so you don't leave your playspace and bump into furniture and walls. But in most mixed reality apps it's superfluous, since you can already see the environment around you, and downright annoying because it means you can't utilize your full room as a playspace.
Since v57 of the Meta XR Core SDK select whitelisted developers have been allowed to disable this boundary. Now with v66 of the SDK, any developer can do this.
The only "catch" is that the boundary will only be disabled while passthrough is being rendered, i.e. in mixed reality. Fully immersive VR still requires the boundary, which makes sense for safety reasons given you can't see your surroundings.
You may be thinking a developer could render a tiny slice of passthrough to trick the system to get rid of the boundary in almost-full VR. But while this technically might work, remember that Quest lowers the CPU and GPU clock speeds when passthrough is active, so this would come at a notable cost to performance.
Before Quest 3 launched clips found in the firmware suggested Meta would replace the boundary with something altogether different, a more intelligent system that showed a mesh of furniture and walls as you approached them. That didn't happen, or at least hasn't yet, but in the meantime getting rid of the annoying legacy boundary in mixed reality will be greatly appreciated by developers and users alike.