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Not sure if this is what you're looking for here, but I'm able to pick my apple studio display as a device on my iPad. Playing Spotify on my iPad right now through the Apple Studio Display speakers and can control volume, pause / play, and skip tracks...it's terrific.
 
Not sure if this is what you're looking for here, but I'm able to pick my apple studio display as a device on my iPad. Playing Spotify on my iPad right now through the Apple Studio Display speakers and can control volume, pause / play, and skip tracks...it's terrific.
Check your devices listed on appleid.apple.com. Is your display listed?
 
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