Try with these settings:

incoming IMAP: imap.aol.com, 993, SSL/TLS, OAuth2, email address

outgoing SMTP: smtp.aol.com, 465, SSL/TLS, OAuth2, email address

Remove the entries for the account from Saved Passwords in Settings, restart TB, enter the account (not app) password in the OAuth window when prompted.

My Thunderbird already has these settings. I removed the entries from Saved Passwords, restarted, entered the account password. But again received the message ""Login to server imap.aol.com with username Leisterr8@verizon.net failed." I have two aol.com accounts and I checked the passwords for those accounts. Both are current. I can log into them at mail.aol.com, but not in Thunderbird. Also, there are now no Saved Passwords. Problem not solved.

I drafted a message in my account on Thunderbird, and Thunderbird opened an aol window, which allowed me to change my passwords (two-step verification required with code). I successfully changed the password, but when I tried to change the password in Thunderbird, it failed.

You shouldn't have to manually change passwords or their OAuth equivalent in TB. As long as cookies are accepted in TB (not browser), an oauth:// token will be automatically stored in Saved Passwords once the OAuth2 authentication completes. Change passwords through the AOL webmail settings, remove old entries from Saved Passwords, restart TB, enter the new password in the OAuth window.

I have new passwords in AOL webmail. I removed the old Saved Passwords. I restarted and entered the passwords again. But the passwords are not accepted. Is there information in Troubleshooting?

Did you enter the password in the OAuth browser-like window, or in a dialog box like the attached picture?

In the dialog box. Where is the OAuth window?

I'm looking at account settings in TB. And I see under security settings in server settings. See attached. Should I change this to OAuth2?

Yes, change it to OAuth2 for all AOL incoming and outgoing servers, as in my first reply. You should have separate smtp servers for each account.

For one account I was able to change the incoming and outgoing server settings to OAuth2. But the second account does not offer the option

Post the settings for the second account.

outgoing SMTP: smtp.aol.com, 465, SSL/TLS, Normal password, email address incoming IMAP: imap.aol.com, 993, SSL/TLS, OAuth2, email address

Change the outgoing authentication to OAuth2.

I do not have that option. Please see attached screen shot.

Use smtp.aol.com for the server name, not smtp.verizon.net.

Ahhhh! Yes, I missed it. Thanks. I changed it to smtp.aol.com for the server name and it works with OAuth2.