It states that
For most UIKit classes, the default (
isAccessibilityElementflag) istrue, but for UILabel it’sfalse.
which is not true:
Labels are accessible to VoiceOver by default.
(UILabel | Apple Developer Documentation)
What I noticed is that an UILabel with no text, indeed has the flag set to false, but if the text property is set, the flag gets set to true with no additional changes.