If you’re using GMail / GSuite using legacy password based authentication it will stop working on 30th May 2022.
To help keep your account secure, starting May 30, 2022, Google will no longer support the use of third-party apps or devices which ask you to sign in to your Google Account using only your username and password.
To continue using Email from ERPNext you need to setup app-specific password.
The process is described in the docs page here: https://docs.erpnext.com/docs/v13/user/manual/en/setting-up/email/email_account_setup_with_gmail (it will also be linked as alert on email account page in next release)