fixed mine doing this
For me the problem seemed to be that my phone and oculus were on different wifi's (phone on 2.4ghz and oculus on 5ghz). THe exact steps I took were below, but I suspect this is what the problem was. If it doesn't fix it try the below:
Opening phone App
going to settings -> clicking my oculus quest 2 so it said connected
Clicking the casting icon in top right of screen (it gave me message that they needed to be on same wifi)
Connected them to same wifi and casting now shows connected.
Restarted Quest 2, and viola, no more error messages.