The code available for download at : https://developer.apple.com/documentation/mapkit/mapkit_annotations/annotating_a_map_with_custom_data
Does not work, line 18 of CustomAnnotationView.swift :
private let blurEffect = UIBlurEffect(style: .systemThickMaterial)
returns with error that :
Type 'UIBlurEffect.Style' has no member 'systemThickMaterial'
Forgot to add my M1 Chip MacBookAir is running Xcode version 12.5.1 (12E507)
As far as I tried, it compiles without any problems with Xcode 12.5.1 on Intel Mac mini (2018). So, it might be the M1 Mac only issue and you should better send a bug report soon. The official documentation of systemThickMaterial does not have any descriptions about unavailability on M1 Mac.
Compiles cleanly, and runs fine for me.
I suggest you try the usual fixes... clear the Derived Data folder, restart everything...