I’m not sure why this has just started happening now, but I’m also seeing the same behaviour on iOS 16. Adding the inter-app-audio entitlement seems to allow the AudioPluginHost to discover third-party AUv3 plug-ins.
This has been discussed previously on the forum, but none of the team has been able to reproduce the problem until now:
I’ll update the Projucer and CMake so that this entitlement is automatically added for iOS AU hosts.