So to confirm, you have accessed the Edit SMTP Server List entry, and have verified and re-entered settings there?
Mail has two sets of credentials and host names and related settings, one for POP or IMAP and receiving and reading mail, and a second set for SMTP or ESMTP and sending mail.
POP or IMAP working and SMTP or ESMTP not working is not at all surprising. It's quite common.
In this case, your sending settings do not match the Yahoo requirements.
Check the SMTP host name, and the username and password.
By all appearances, your SMTP server settings are incorrect.
App Passwords are not related to Yahoo SMTP login credentials.