您可以通过设置"登录已阻止"来暂时阻止用户登录对于O365管理中心的此用户 - 请参阅

阻止前员工访问Office 365数据。但正如文档所述，这些更改可能需要24小时才能生效：

in Sharepoint Online you may temporary prevent user from being able to login by setting "Sign-in blocked" for this user in O365 admin center - see Block a former employee's access to Office 365 data. But as documentation says it may take up to 24h these changes to take effect:

"阻止帐户最多可能需要24小时才能生效。"如果您需要立即阻止用户的登录访问，则应重置其密码，然后启动一次性事件，以便在所有设备上签署Office 365会话之外"。

"Blocking an account can take up to 24 hours to take effect. If you need to immediately prevent a user's sign-in access, you should reset their password and then initiate a one-time event that will sign them out of Office 365 sessions across all devices".