With the official iOS 14 release the problem is not fixed. But I found out something interesting.
AirPlay is working on Airport Gen 2 (2012) devices. But not on Gen 1 device. So I assume that Apple just shut down the support for those old Airport Express devices. What means that they can now be thrown away?
Lupo92
Users receive reputation points by contributing quality content to the forums.
Posts include post and replies published on the forums.
Post authors can mark replies as Accepted to indicate successful solutions.
Apple Developer Forums admins can mark replies as Apple Recommended to indicate an approved solution
From
Erfurt, Deutschland
Post
Replies
Boosts
Views
Activity
Still not working for me on iOS 14 Beta 7.