我在 Excel VBA 測試過
Workbooks.Open "test2.xlsx"
Set wbWeb = Workbooks("test2.xlsx")
或是你的寫法
Workbooks.Open filePath
Set wbWeb = Workbooks(filePath)
我這樣寫沒問題
Sub test()
    Dim wbWEB As Workbook
    Dim filename As String
    
    filename = "D:\Desktop\xxx.xlsm"
    
    Set wbWEB = Workbooks.Open(filename)
    
End Sub