I've tried to manually lock the device while airplay mirroring -- Interrupted airplay Tried using automatic lock by _ minutes -- It won't execute while airplay mirroring Is there any way to set iDevices to go in black screen while airplay mirror

This is a bit of a long shot but there is a feature in Voice Over that allows you to turn off the screen by triple tapping the screen with three fingers. I have never tried this so I don't know if mirrowing will continue after you turn the screen off. It take a few steps to set up so let me know if you're interested in trying.

Here's the instructions if you want to give it a try.

Go to settings> general> accessibility> accessibility shortcut> Voiceover. This allows you to turn Voiceover on/off by triple tapping the home button.

After you check VoiceOver(see screenshot) triple click the home buttom to turn Voiceover on. Then triple tap the screen in accessibility shortcut where I placed the x. The screen should turn off. Now you can turn control screen curtain on/off by triple tapping the home button.

If all works to plan start your mirrowing then triple tap the home button three time to turn on screen curtain