Fix: iPhone mirroring always times out

iPhone mirroring stopped working after I reset my iPhone network settings. To fix it, delete all settings for iPhone mirroring:

defaults delete com.apple.ScreenContinuity

Thanks to drakcrestron229 in the Apple Support Community.

Symptoms

• The initial connection would always time out and fail
• "Reset iPhone Access" in iPhone Mirroring settings always failed
• The app was still able to detect when my phone was in use
• iPhone widgets on my MacOS desktop still worked

What didn't work

• rebooting both devices several times
• toggling the WiFi private address settings on both devices
• toggling WiFi and bluetooth on both devices

Details

Every time I tried to connect, it went through the motions, prompted for Touch ID, and even notified me if my iPhone was in use, but it would always time out after ~2s when trying to connect. "Reset iPhone Access" in the settings would also fail.

Looking at streamed logs in at the Console app, it seemed to complain about not being able to find the correct bluetooth address. I'm guessing it remembered some Bluetooth address from the first time I had set up mirroring and it wasn't set up to handle a change. Deleting all settings was the only thing that worked.