You need to generate an app password to be able to use an AOL Mail account with K-9 Mail. See Create and manage third-party app passwords - AOL Help
Then use the following server settings when adding the account to K-9 Mail:
IMAP (incoming server)
- IMAP server: imap.aol.com
- Security: SSL/TLS
- Port: 993
- Username: YourUsername@aol.com (or @love.com, @games.com, etc.)
- Password: The generated app password
SMTP (outgoing server)
- SMTP server: smtp.aol.com
- Security: SSL/TLS
- Port: 465
- Require sign-in: Yes
- Username: YourUsername@aol.com (or @love.com, @games.com, etc.)
- Authentication: Normal password
- Password: The generated app password