You could do something along these lines I guess.<br>
If the file is encrypted it will pass and the password can be requested.<br>
If it's not, it will error and the file can be loaded normally.<br>
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)

import msoffcrypto
file_c = msoffcrypto.OfficeFile(content) 
is_pwd_protected = file_c.is_encrypted()  # 如果文件受密码保护，is_encrypted将返回True。