Following this to see if anybody offers one. Biggest issue I think will be keeping the Bluetooth or WiFi connection active without music playing (I assume you want this for a music alarm). I’m currently using an old iPhone 6s connected to the aux in (RCA) on an old Bose Wave radio, with a music alarm app on the iPhone. I’ve been using this same setup with retired iPhones for years to play music playlists as alarm music. Any attempt I’ve made to play the alarm music wirelessly through airplay to Airport Express or recently to HomePod is unreliable since it loses the connection overnight. I wish I could find or figure out how to do it successfully, maybe using a shortcut triggered by an alarm app.