Again_au fails to compile

Xcode 12.4 and Xcode 12.2, VST SDK 3.7:
Suddenly I cannot longer compile again_au or any other AU wrapper.

PhaseScriptExecution CMake\ PostBuild\ Rules /Users/markuskrause/VST_SDK_3.7/build/public.sdk/source/vst/auwrapper/again/vstsdk.build/Debug/again_au.build/Script-45B8A0C2C8D3442685735112.sh (in target ‘again_au’ from project ‘vstsdk’)
cd /Users/markuskrause/VST_SDK_3.7/VST3_SDK
/bin/sh -c /Users/markuskrause/VST_SDK_3.7/build/public.sdk/source/vst/auwrapper/again/vstsdk.build/Debug/again_au.build/Script-45B8A0C2C8D3442685735112.sh

/Users/markuskrause/VST_SDK_3.7/build/VST3/Debug/again_au.component/Contents/Resources/plugin.vst3 → /Users/markuskrause/VST_SDK_3.7/build/VST3/Debug/again.vst3
/Users/markuskrause/Library/Audio/Plug-Ins/Components//again_au.component → /Users/markuskrause/VST_SDK_3.7/build/VST3/Debug/again_au.component
failed to find AudioUnit/AudioUnit.r
/Users/markuskrause/VST_SDK_3.7/VST3_SDK/public.sdk/source/vst/auwrapper/again/…/auresource.r:37: ### Rez - kCFHostErrorUnknown / kCFStreamErrorSOCKS4SubDomainResponse / kCFStreamErrorSOCKS5BadState / kCFStreamErrorDomainMacOSStatus / siInitVBLQsErr / dsAddressErr / scCommErr / ENOENT (2) during open of “AudioUnit/AudioUnit.r”.
Fatal Error!
/Users/markuskrause/VST_SDK_3.7/VST3_SDK/public.sdk/source/vst/auwrapper/again/…/auresource.r:37: ### Rez - Fatal Error, can’t recover.
/Users/markuskrause/VST_SDK_3.7/VST3_SDK/public.sdk/source/vst/auwrapper/again/…/auresource.r: ### Rez - Since errors occurred, /Users/markuskrause/VST_SDK_3.7/build/VST3/Debug/again_au.component/Contents/Resources/again_au.rsrc’s resource fork was not completely updated.
Command PhaseScriptExecution failed with a nonzero exit code

The problem seems to affect also Juce:

I’ve seen these as well, independent of the VST3 SDK. It seems like Apple has finally abandoned Audio Unit v1 for good. However, all machines that can run the “new” libc++ (10.9 and later) used in the current SDKs also rely on Audio Unit v2 so it should be save to simply remove all the obsolete rez stuff.
I’ve done that for JUCE here:

I messed around for another 2 days and still couldn’t make the AUwrapper work. We get a massive number of customers requesting an AU version.
It would be nice if Steinberg could offer some help and take a look at it, since it is clearly a problem of the VST SDK that affects many developers

Maybe I’m missing one step, but I can successfully build the again_au target on macOS 11 on M1 and it runs perfectly at least in Garageband (both the Rosetta translated one and the native one).
Did you by any chance use another SDK than the one included in Xcode? That would explain your issue.