I have not seen any sensible answers to this question, but I have been having a similar problem. iPhone 11 Pro running 16.3.1. I (used to) regularly AirPlay to 2 different Samsung Q Series TVs on quite different networks.
somewhat recently, possibly with the upgrade to 16.3, AirPlay to both these TVs has not been working. My own investigation stumbled across a solution!!
- Go to Settings> WiFi> and tap the ⓘ information symbol, then turn off "Private Wi-Fi Address".
- Return to your home screen and retry AirPlay - worked for me first time!
- I then turned the Private Wi-Fi Address back on, and AirPlay again started as normal
There are a few Apple Support articles on "Private Wi-Fi Address", and reading between the lines it could could be the cause of the AirPlay problems many of us have been having with Samsung TVs?
Give the instructions above a go - it worked for me, Steve
Use private Wi-Fi addresses on iPhone, iPad, iPod touch, and Apple Watch - Apple Support