Probably something like this? (UNTESTED)
Sub Sample()
Dim strWB4, strMyMacro
strMyMacro = "Sheet1.my_macro_name"
'
'~~> Rest of Code
'
'loop through the folder and get the file names
For Each Fil In FLD.Files
Set x4WB = x1.Workbooks.Open(Fil)
x4WB.Application.Visible = True
x1.Run strMyMacro
x4WB.Close
Do Until IsWorkBookOpen(Fil) = False
DoEvents
Loop
Next
'
'~~> Rest of Code
'
End Sub
'~~> Function to check if the file is open
Function IsWorkBookOpen(FileName As String)
Dim ff As Long, ErrNo As Long
On Error Resume Next
ff = FreeFile()
Open FileName For Input Lock Read As #ff
Close ff
ErrNo = Err
On Error GoTo 0
Select Case ErrNo
Case 0: IsWorkBookOpen = False
Case 70: IsWorkBookOpen = True
Case Else: Error ErrNo
End Select
End Function