As others have said, the v4 has never had RTSP. Can you clarify?
If you were using it with Tiny Cam or possibly Docker Wyze Bridge (neither of which uses RTSP to the cam, but they can convert the cam feed to RTSP for you) or something like that, then you may need to downgrade the firmware, the most recent has new authentication that is not compatible with many 3rd party apps.
For Tiny Cam, I believe they have released an update to support the latest v4 firmware. Have you updated Tiny Cam (if that’s what you’re using).
For others, you’ll need to follow the instructions to manually downgrade to a previous firmware, and turn off auto updates until those developers add support for it.
There are several other threads about this - below is one of them for reference but you can find others in the search. The end result is basically the same (what I’ve said above)