Exactly the same issue here on both my iPhone 12 Pro (14.2.1) and iPad Pro 12.9 3rd Gen (14.3 public beta second release). Just finished a call with Apple tech support. We ran through all the troubleshooting [reset all settings, reset network settings, reset my wi-fi network, reset my airplay devices (homepods, stereo) signing both devices out of iCloud, hard reset] but problem persists. They said that the next step is to set up the devices as new (not restore from a back-up) and see if Airplay will work, then restore from backup and see if Airplay works. Apparently Apple will only send the issue to senior software support if Airplay is not working while set up as a new device. If it ends up being an issue with my particular iphone & ipad set-up (i.e. the back-up version), there’s no further support available. Seems short-sighted, since most people are not starting from scratch each time they get a new device or update iOS, but I guess this is Apple’s triage method. I’m still syncing my iCloud after logging out during troubleshooting, but as soon as that’s done, I’ll try a clean set-up and report back...