Maybe something like this (use a copy in case it fails)

Sub fixme()   Dim otxR As TextRange2
   Dim otRtarget As TextRange2
   Dim osld As Slide
   Dim L As Long
   Dim C As Long
   Dim oshp As Shape
   On Error Resume Next
   For Each osld In ActivePresentation.Slides
      For Each oshp In osld.Shapes
         If Not oshp.Type = msoPlaceholder Then
            If oshp.HasTextFrame Then
               If oshp.TextFrame.HasText Then
                  For L = oshp.TextFrame2.TextRange.Paragraphs.Count To 1 Step -1
                     Set otxR = oshp.TextFrame2.TextRange.Paragraphs(L)
                     For C = 1 To otxR.Characters.Count
                        If Asc(otxR.Characters(C)) = 13 Then
                           otxR.InsertAfter Chr(11)
                           otxR.Characters(C).Delete
                        End If
                     Next
                  Next L
               End If
            End If
         End If
      Next oshp
   Next osld
End Sub