Thank you very much to Neil and HPSoln, you two hitted the spot!
Here I leave you another option I found on internet.
And please, sorry for the delay 😕
Regards!
Sub SelectLayersInDisplayView()
' selects all of the layers in the first data frame in the TOC's display view
Dim pMxDoc As IMxDocument
Set pMxDoc = ThisDocument
Dim pTOC As IContentsView
Set pTOC = pMxDoc.ContentsView(0) ' Display View
Dim pMaps As IMaps
Set pMaps = pMxDoc.Maps
Dim pMap As IMap
Dim i As Integer
Set pMap = pMaps.Item(0) ' first data frame
Dim pEnumLayer As IEnumLayer
Set pEnumLayer = pMap.Layers(, False) ' we will not select layers within group layers
Dim pLayer As ILayer
Set pLayer = pEnumLayer.Next
pTOC.RemoveFromSelectedItems pTOC.SelectedItem
Do While Not pLayer Is Nothing
pTOC.AddToSelectedItems pLayer
pTOC.Refresh pLayer
Set pLayer = pEnumLayer.Next
Loop
End Sub
Sub SelectDataFrameInSourceView()
' selects the first data frame in the TOC's source view
Dim pMxDoc As IMxDocument
Set pMxDoc = ThisDocument
Dim pTOC As IContentsView
Set pTOC = pMxDoc.ContentsView(1) ' Source View
Dim pMaps As IMaps
Set pMaps = pMxDoc.Maps
Dim pMap As IMap
Set pMap = pMaps.Item(0) ' first data frame
pTOC.SelectedItem = Nothing
pTOC.SelectedItem = pMap
pTOC.Refresh pMap
End Sub