I don't think you can directly disable the gizmo. Only switching a tab other than Create will hide the gizmo.
I checked whether it is possible to write a modifier in MAXScript that derives from Extrude modifer but does not show the gizmo. Unfortunately that seems not to be possible, you would need to write a full 3ds Max plugin using C++ for that.
The team was made aware of some users being unhappy with the new extrude gizmo but I cannot make any promises on whether or when this will be fixed.
Actually it would be generally a nice modifier option to be able to hide the gizmo...
Martin B
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