ダウンロードして確認してみたら、Xcode 12.0.1にはシミュレータ向けのAVFoundation.swiftmoduleが入ってないな。

$ export DEVELOPER_DIR=/Applications/Xcode_12.0.1.app; diff -u $(xcrun --show-sdk-path -sdk iphoneos)/usr/lib/swift/AVFoundation.swiftmodule/arm64.swiftinterface $(xcrun --show-sdk-path -sdk iphonesimulator)/usr/lib/swift/AVFoundation.swiftmodule/x86_64.swiftinterface diff: /Applications/Xcode_12.0.1.app/Contents/Developer/Platforms/iPhoneSimulator.platform/Developer/SDKs/iPhoneSimulator14.0.sdk/usr/lib/swift/AVFoundation.swiftmodule/x86_64.swiftinterface: No such file or directory