Compare sheets and put missing rows into third sheet.

Sub Diffs()

    Dim lr As Integer
    Dim fValue As Range
    Dim c As Range
    
lr = Sheet1.Range("A" & Rows.Count).End(xlUp).Row

Application.ScreenUpdating = False

Sheet3.UsedRange.ClearContents
Sheet3.Rows(1).Value = Sheet1.Rows(1).Value
Sheet1.Range("A2:C" & lr).Copy Sheet1.[BA2]

For Each c In Sheet1.Range("A2:A" & lr)
    Set fValue = Sheet2.Columns("A:A").Find(c.Value)
        If fValue Is Nothing Then GoTo Nextc
            If c.Value = fValue.Value Then
                Range(c, c.Offset(0, 2)).ClearContents
          End If
Nextc:
Next c

For Each c In Sheet1.Range("A2:A" & lr)
    If c.Value <> "" Then
         Sheet1.Range(Cells(c.Row, "A"), Cells(c.Row, "C")).Copy Sheet3.Range("A" & Rows.Count).End(3)(2)
         End If
    Next c
     
Sheet1.Range("BA2:BAC" & lr).Copy Sheet1.[A2]
   
Application.CutCopyMode = False
Application.ScreenUpdating = True

End Sub