I’ve recently recompiled TDBGrid component, to implement several custom functions, altho i’ve noticed that the feature of extra design-time context menu item “Columns editor” is gone now.

I’ve failed to find any code which creates this menu in original Vcl.DBGrids unit and had a really bad luck looking for a solution online on how to do this.
This also applies to double-clicking. It used to call Columns Editor, now it just creates OnCellClick event.
In your design time package for the component, implement a component editor:
You need to register this component editor also. Call
RegisterComponentEditorin yourRegisterprocedure to do so: