Have you looked in this long arsed thread, much of it applied when only SD flash was the thing.
Quite a few references and things to try for being stuck in the username password loop.
Does SD flash still work? I’m asking because I don’t know. Could try that if it does.
AHA! I never mentioned it, but my issues are at work, on a Ubiquiti wireless network. I have a couple Wyze Cam v3 at home, and last night I tried to set up RTSP and it all worked like a charm, no issues whatsoever. So, my issue is clearly related to the Ubiquiti network at work. So far this morning I have had no success, but at least now I know I’m not losing my mind.
(By the way, I’m not using UniFi Protect, just a bog standard wifi network using Ubiquiti AC-Pro units.)
Anything from Packet Capture for those devices?
You should be able to see the traffic to/from those devices. I believe they route to a cloud based system to validate their authorization. I dont know offhand what IP space those cloud servers run or their locations but you could be locked down from that aspect.
No packet capture yet, but I’ll get that going; thanks for the suggestion.
tl;dr: Set “Forward Unknown Multicast Traffic” to “Flood” on the network(s) for the cameras and monitor stations, in Ubiquiti Network Application → Settings → Networks.
Alright, I got this fixed. First off, is RTSP multicast or unicast? For some reason, this question lingers over me any time I have trouble with RTSP traffic of ANY sort. I know it’s unicast, but this question is what led me to the fix.
In the Unifi Network Application → Settings → Networks, there is an option to “Forward Unknown Multicast Traffic”. Since deploying Ubiquiti access points years ago, I’ve had this set to “Drop”. I just changed it to “Flood” and selected the Default network (which is configured for IGMP snooping), and BAM, RTSP setup on my Cam v3 cameras works immediately. SUCCESS.
Thanks for coming along with me on this journey of discovery. 
fyi, im enrolled in the beta program, i had a v3 4.36.8.15 fw released December 2021, and i was able to to do multiple updates right upto the rtsp beta fw 4.36.16.5654 successfully, all within the official wyze app, i enabled rtsp and i could change wifi ssid within the app, no sdcard flash needed. tried it with my other v3 but i could not stream or log into it after first update request, meaning i have to go on a ladder, winter here, and hit the reset button