Based on the packages used some thoughts/discussion points:

• I expect MRTK3 UI to work out of the box
• I suggest MRTK3 Input package should migrate/support Unity's XR Hands package. Hopefully not a huge task, see: https://localjoost.github.io/Getting-Unity-XR-hands-to-work-on-HoloLens-and-Quest-in-a-bare-bones-project/
• There is no mention of OpenXR and instead seems to be ARFoundation (ARKit) - so some app changes required but given that minimal work is required to get an MRTK3 app running on ios/android with ARFoundation I expect this to also be mostly out of the box.

For early testing, you can apply to Unity's beta program: https://create.unity.com/spatial

Disclaimer: Not a core MRTK contributor

Thank you @njannink , at this time we have no plans to support Apple Vision Pro. However, community contributions are welcome, and we encourage the community to add this support.

Needs to be reconsidered MixedRealityToolkit/MixedRealityToolkit-Unity#88