This question looks old, I faced the same recently. It seems like after a few months it removes testers once all builds expire from a test flight. It was fixed after I added a new test flight builds, it took longer than normal before it notify my internal testers approx 2hours but, eventually, it added them back and notify them of the new build version. No need to delete all users and re invite.

Hi Guys, I tried all the steps. It gives me a code but once I enter it doesn't show connect on my Xcode, but I can see my Mac name in Vision Pro under the remote device. Also, I don't see a developer mode option under the privacy menu. I using Intel Mac, too with Xcode 15.2 Anyone has found solution?

You need an Apple silicon Mac to deploy on an Apple Vision Pro device. It doesn't connect with the Apple Intel chip even in Xcode 15. https://developer.apple.com/documentation/visionos Raise a request to Apple to support Intel Macs.