2 issues:

• the app is missing the permissions for notifications (AndroidManifest.xml)
• the native notification with custom Actions or a Reply Action throws an

Java.Lang.IllegalArgumentException:
com.CompanyName.Avalonia.Labs.Catalog: Targeting S+ (version 31 and above) requires that one of FLAG_IMMUTABLE or FLAG_MUTABLE be specified when creating a PendingIntent.
Strongly consider using FLAG_IMMUTABLE, only use FLAG_MUTABLE if some functionality depends on the PendingIntent being mutable, e.g. if it needs to be used with inline replies or bubbles

It turns out, the NativeNotification always requires FLAG_MUTABLE in those cases so the sample works.