I just got this working again. The new feeds from Unifi Protect look something like this:
rtsps://192.168.1.2:7441/asdf1234?enableSrtp
To convert this to a stream URL that Monocle can use, do the following:
Change rtsps to rtsp
Change port 7441 to 7447
Remove ?enableSrtp
So for my example above:
rtsp://192.168.1.2:7447/asdf1234
In my case it was the last bullet point that I was missing and it caused the stream to hang in an Echo Show.