我想你可以沿着这条线做点什么。
如果文件被加密，它将通过，并且可以请求密码。
如果不是，则会出错，文件可以正常加载。

import openpyxl
import io
import msoffcrypto
from msoffcrypto.exceptions import FileFormatError  # pip install msoffcrypto-tool

filename = 'foo.xlsx'

with open(filename, 'rb') as file:
    try:
        workbook = io.BytesIO()
        office_file = msoffcrypto.OfficeFile(file)
        print("File is password protected")
        passwd = input("Please enter file password")
        office_file.load_key(password=passwd)
        office_file.decrypt(workbook)
    except FileFormatError as e:
        print(e)
        print("File is not password protected")
        workbook=filename

    wb = openpyxl.load_workbook(workbook)
    ws = wb['Sheet1']

    print(ws['A1'].value)