Option Explicit

Public Function JoinText(cells As Variant, Optional delim_str As String) As String
    If cells.Columns.Count < cells.Rows.Count Then
       JoinText = Join(WorksheetFunction.Transpose(cells), delim_str)
    Else
       JoinText = Join(WorksheetFunction.Transpose(WorksheetFunction.Transpose(cells)), delim_str)
    End If
End Function

=HVIS(B2=1, JoinText(C2:INDIREKTE("C"&SAMMENLIGNE(A2,A:A,1)),"|"), "")

=IF(B2=1, JoinText(C2:INDIRECT("C"&MATCH(A2,A:A,1)),"|"), "")