There are no similar events in PowerPoint. You would really need to write a with events class but this isn't simple and difficult to make work outside of an AddIn. IF you are accessing vba during the show (sounds like it) then there is a solution.

Sub OnSlideShowTerminate(ByVal Wn As SlideShowWindow)
Dim osld As Slide
Dim opres As Presentation
Set opres = ActivePresentation
For Each osld In opres.Slides
' insert code here to clear textbox
On Error Resume Next
' will depend whether it's an ActivX box or a normal textbox
'for ActivX
osld.Shapes("TextBox1").OLEFormat.Object.Text = "" ' use actual name of course
'normal shape
osld.Shapes("name of shape").TextFrame.DeleteText
Next osld
End Sub

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