Si en réalité tu ne veux sélectionner qu'un seul fichier, alors c'est une incompréhension de ma part, je vais modifier la macro.
Option Explicit
Dim wbk1 As Workbook, wbk2 As Workbook
Dim ws1 As Worksheet, ws2 As Worksheet
Dim monFichier As Variant, derL%, onglet$
Sub collecter()
onglet = "Feuil1"
monFichier = Application.GetOpenFilename("Fichiers Excel (*.xlsx), *.xlsx")
If monFichier = False Then Exit Sub
Set wbk1 = ThisWorkbook
Set ws1 = wbk1.Sheets(onglet)
ws1.Cells(Rows.Count, 1).End(xlUp).Offset(1, 0).Select
derL = ws1.Cells(Rows.Count, 1).End(xlUp).Row + 1
Workbooks.Open Filename:=monFichier
Set wbk2 = ActiveWorkbook
Set ws2 = wbk2.ActiveSheet
ws2.Range("A1").CurrentRegion.Offset(1, 0).Cells.Copy
ws1.Paste
Application.DisplayAlerts = False
wbk2.Close False
Application.DisplayAlerts = True
derL = ws1.Cells(Rows.Count, 1).End(xlUp).Row
ActiveSheet.Range("$A$1:$F$" & derL).RemoveDuplicates Columns:=Array(1, 2, 3, 4, 5, 6), Header:=xlYes
derL = ws1.Cells(Rows.Count, 1).End(xlUp).Row
Range("A" & derL).Select
End Sub