EyeonTips:Script/Reference/Applications/Fusion/Classes/Composition/SetActiveTool
From VFXPedia
To deselect all tools, omit the parameter or use nil (LUA) or None (Python):
-- deselect all comp:SetActiveTool(nil)
To deselect all tools, omit the parameter or use nil (LUA) or None (Python):
-- deselect all comp:SetActiveTool(nil)