cant log in to yahoo accounts, get SASL error.

That error is often a result of incorrect security settings. Confirm your server settings. Here are my working ones for comparison:

My Yahoo settings:

Incoming Server Type: IMAP Mail Server Incoming Server Name: imap.mail.yahoo.com Port: 993 User Name: <my email address> Connection Security: SSL/TLS Authentication method: OAuth2

SMTP Server Name: smtp.mail.yahoo.com Port: 465 Connection Security: SSL/TLS Authentication method: OAuth2 User Name: <my email address>

My Yahoo settings:

Incoming Server Type: POP Mail Server Incoming Server Name:POP.mail.yahoo.com Port: 993 User Name: <my email address> Connection Security: SSL/TLS Authentication method: OAuth2

SMTP Server Name: smtp.mail.yahoo.com Port: 465 Connection Security: SSL/TLS Authentication method: OAuth2 User Name: <my email address>

3 different email addresses that are years old stopped working in Thunderbird, they work ok on phone with yahoo mail. No settings were changed. another email from gmail set up as IMAP works ok on Thunderbird. unable to change from POP to IMAP in Thunderbird.

Please quote all error messages you see, in full, verbatim. Screen shots would suffice.

This might be relevant:

OAuth2 Authentication for Yahoo, AOL and ATT

https://support.mozilla.org/en-US/kb/thunderbird-and-yahoo