Formatting Multiple Series in a Chart

This change works for me,

Sub x()
    Dim objSeries As Series
    
    With ActiveChart
        For Each objSeries In .SeriesCollection
            With objSeries.Format.Line
                .Style = msoLineSingle
                .Transparency = 0
                .ForeColor.RGB = RGB(40, 56, 24)
                .Weight = 0.75
            End With
        Next
    End With
End Sub