There are a handful of specific contexts in which a Unity-made app might appear on visionOS. 2D apps running in a flat window within the user's space will be the easiest to implement.

“Unity-based apps and games run natively on Apple Vision Pro, ... One such example is What the Golf?, a crowdfunded game launched as part of Apple’s Arcade offering in 2019 ...

With these tools, apps can take advantage of Unity’s technology known as “PolySpatial” to display 3D elements that interact with the real world. Unity tools now available for Apple Vision Pro.

And Unity, maker of the most popular game engine for XR app developers, announced they’ve partnered with Google to provide official platform support for Android XR.