With these changes it should work better.
Option Explicit
Private Sub Workbook_Open()
    Dim d1     As Date
    Dim d2     As Date
    Dim password As String
    d1 = CDate("10/02/2021")
    d2 = Date
    If d2 > d1 Then
        password = InputBox("enter password")
    Else
        MsgBox ("Opening file")
        Exit Sub
    End If
pwd:
    If password = "abC123_" Then
        MsgBox ("Welcome!")
        Exit Sub
    Else
        MsgBox ("Incorrect password!")
        password = InputBox("enter password again")
        If password = "" Then
        MsgBox ("No password ... no party ...")
        ThisWorkbook.Close False
        End If
        GoTo pwd
    End If
End Sub