On the website where one can apply to use the iOS closed beta, it should list the new iPhone 16/16 Plus, 16 Pro/Pro Max.

These are the newest iPhones available from apple.com that has an A18 chip and I think VRChat work for those.

I personally think however that only allowing VRChat on 16 Plus, Pro and Pro Max could also be an option if it is decided that the normal 6.1 inch screen is too small (the Pro is 6.3 inch, the Plus is 6.7 inch, while the Pro Max is 6.9 inch. I recently got a 16+ and would love to test my new iPhone to it's absolute limits using the VRChat closed beta but ran into this problem.