problem with Google sign-in on macbook Pro with High Sierra OS

Hello Redeemed5777,

Thanks for using Apple Support Communities. Since the error message mentions security, this is likely due to Google's security requirements. As mentioned in the following section of If Mail on your Mac keeps asking for your password - Apple Support, enabling two-step verification may help comply with those requirements.

"Why is Mail asking for your password?

Mail asks for your password when it can connect successfully to your email provider, but can't connect to your email account because your email provider isn't accepting your email password.

Your email provider may reject your password for several reasons, including:

• You're not using your current email password. If you updated the password on another device, make sure that you're using the same password on your Mac.
• Your email provider needs you to update or reset your password for security reasons. For example, if you're using Google’s two-step verification, your Gmail account in Mail requires the appropriate app-specific password.
• Your email provider deactivated or suspended your account. Contact your email provider for help."

If the same continues, you can reach out to Google as they'll be in the best position to provide further support. You can also access your email through Google's webmail if you're unable to add it to the Mail app.

Take care.