Actually it's a member of msforms library, not from native vba.

you'll need a reference to Microsoft Forms Object Library. The reference is automatically added
to a workbook when you insert a Userform from VBeditor's Insert menu.

Ok, cool

I added a userform then deleted it just after.
But the reference stay !

Hard to know when you just reed the VBA Help ! this seems to be a
"regular" VBA stuff...