The FMX.TGrid-Items Editor-Delete button is not available in the descendant form.

[dmitrybv 1]

Embarcadero® RAD Studio 12 Version 29.0.51961.7529
If you create an empty Form in the FMX project,
then create a descendant of this Form
Then place a TGrid component on the Descendant Form

Then open the Items Editor for TGrid and add several columns, then the Delete button in the Items Editor window becomes unavailable, and it is always unavailable so that it is not possible to delete columns from the TGrid component.

 

Most likely the problem is related to the code
 

unit FMX.Design.Items;
…
btnDelete.Enabled := Editable and (Designer.GetAncestorDesigner = nil) and (ItemsTree.Selected <> nil);