In my excel sheet I put 2 OptionButton objects:
in my VBA macro I added:
Sub OptionButtonDebugOff_Click()
debugmode = False
End Sub
Sub OptionButtonDebugOn_Click()
debugmode = True
End Sub
and associated the object with resp. OptionButtonDebugOff_Click and OptionButtonDebugOn_Click (right-click on the "button" -> assign macro).
Event handling works fine ('debugmode' variable is changed to False when I click on the 'OptionButtonDedugOff').
I haven't found the VBA command to set a value to those OptionButton's , in particular at macro start, to make the button associated with OptionButtonDedugOff_Click checked (selected) by default (knowing that, besides, debugmode is set false at macro start).
Thanks for your advises!

worksheets("SheetName").Shapes("ButtonName").ControlFormat.Value=xlofforxlonName Boxon the left side next to the formula bar.