The standard was sysdefault. I tried all others as well without any change.
I changed to the basic „simple airplay“ and was able to play a youtube video. Lots of crackling, but the sound of the video was audible.
Then I switched on iTunes and tried to play a song. This made the laptop switch to internal speakers. Trying to choose max2play as output device didn’t work and gave me the error message that max2play is busy and I need to choose another airplay device.
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