Some problems to add email account in CiviMail CiviCRM
First step would be to use Server: imap.gmail.com. smtp.gmail.com is for outgoing mail and Bounce Processing is for checking incoming mail.
Second step would be to verify that Less secure app access is enabled in Gmail.
If that doesn't solve the problem, here are the settings that work for me with Google Apps for bounce processing, same as what you have but using POP instead of IMAP:
Server: pop.gmail.com Protocol: POP3
Optionally, add Local part: myemail+ if you want VERP processing.