Airplay devices cannot be found


I have a problem with my Airplay devices.
In the past I ran the Roon software on an iMac (late 2012). Everything ran very well - all airplay devices worked perfect.

Last week I switched to a Mac mini M1. Now, no airplay devices can be found - only my Vault 2i player.

The core is running on a NAS (DS920+).

Any helpful hints?

thanks a lot and kind regards,