For some unknown reason, this option was removed from iOS 14.5 beta 2, but Apple has re-enabled it with today’s release of iOS 14.5 beta 3.
In addition to letting users set third-party email apps and web browsers as default, iOS 14 included options to change the default player for music, podcasts, and audiobooks on the HomePod.We don’t know why Apple removed this feature from the second beta release of iOS 14.5, but it’s now back with the third beta.Unfortunately, there’s no option in the Settings app to change the default music app, so you have to use Siri every time you want to set another app as the default.