See [How To Use Google's SMTP Server - DigitalOcean|https://www.digitalocean.com/community/tutorials/how-to-use-google-s-smtp-server]

Turn off "use as alias".

Don't forget to specify the SMTP server as {{smtp.gmail.com}}, not something silly like smtp@gmail.com or whatever.

Your username is your full gmail address, {{yourname@gmail.com}}, and the password is an app password you create.

Create an app password for yourself under Google | Manage Account | Security | 2-Step Verification | Account passwords (bottom of page), and use the app password.

Sometimes I have to try twice, so maybe stash the password somewhere for the second try.