Building AUv3's?

Can you please clarify what you mean by "more modern"?

The AUv3 template that comes bundled with Xcode gets modernized regularly embracing the latest changes, such as SwiftUI and C++-Swift-interoperability. That would be the recommended way to build an AUv3.

FWIW The template keeps evolving, I've noticed, and taken advantage of. So one thing to do is just create a new "Audio Unit Extension App" and see what the latest is. For instance, there used to be a framework target, and that's no longer there/necessary.

I do appreciate the template code, and I have built several ‘midi processor’ Auv3s with it. But I am wishing for a tighter integration with swift UI, parameters that use SwiftData, etc. Code like ‘ObservableAUParameterNode’, custom controls like MomentaryButton I was hoping was temporary glue.

CIFilter is an example model/pattern which I enjoy, and actively building/creating with. I create the UI using modern 'Swift' frameworks, and the real-time video processing using metal shaders. Of course in audio real time would be in C.