Hi @Yu Tian,
Kindly note that since WordPress is a third-party product, we may not be very familiar with it.
From the screenshot I suppose the SMTP password here may refer to the app password in Microsoft 365 (Exchange Online).
For how to setup app password please refer to this link:
Manage app passwords for two-step verification
While please note that since app password uses basic authentication, which by default is disabled in the tenant, you may need to contact your tenant admin to check the following (like disabling security defaults but you need MFA enabled for your mailbox) to enable basic authentication for SMTP:
Error: Authentication unsuccessful
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