XCode 12 - applying constraints on stack views

I can't seem to add constraints on stack views.
Only the bottom constraint option is turned on and all other constraint options(top, right, left) are not selectable.

Also I can't seem to align my stack view horizontally or vertically at center to the root view.

Is there a special way to apply constraints to a stack view?
Or is this a bug in xcode 12?
Which constraints do you apply exactly to which objects ?

Usually, the constraints should be on the stack not on objects inside (this is automatically layout).
I have the same problem with label: alignment constraint checkboxes are disabled

XCode 12 - applying constraints on stack views
 
 
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