VBA Code for highlighting cells if it appears elsewhere

Try this:

Sub EF974522_find()
    Dim c, f As Range
    
    For Each c In Sheets("Sheet2").Range("A1", Sheets("Sheet2").Range("A" & rows.Count).End(xlUp))
        Set f = Sheets("Sheet1").Columns(3).Find(c.Value, lookat:=xlWhole)
        If Not f Is Nothing Then c.Interior.Color = 255
    Next
End Sub