Gmail to Apple Mail

Sign in using app passwords

An app password is a 16-digit passcode that gives a non-Google app or device permission to access your Google Account. App passwords can only be used with accounts that have 2-Step Verification turned on.

afton16 wrote:

When I try to add my Gmail account to Apple Mail, I get this error message. The password and email address are correct. Please help!

https://discussions.apple.com/content/attachment/d6e66597-46f1-4ab4-a8bb-a1cee7580ee5

Contact google support since they can't verify your account.