What is the authentication method for the Yahoo mail account, normal password or OAuth2?

What is the authentication method for the Yahoo mail account, normal password or OAuth2?

It's whatever the attached screenshot shows. It's my usersname and a password. Nothing happens when I enter what it asks. It just keeps showing me that dialog.

The authentication method is in Tools/Account Settings, Server Settings for the incoming, and Outgoing Server (SMTP) for the outgoing. But even if you don't have a Yahoo mail account in TB, the setup may fail. I did the following test:

Added a CalDAV calendar for an AOL account (AOL mail is based on Yahoo). The calendar was created in TB, but was unable to sync, and showed an error icon. Adding the same calendar through Manual Configuration in TbSync/Provider for CalDAV & CardDAV, with the same CardDAV URL, it synced and worked as expected, with no errors.

I can't say why your method doesn't work, but suggest you try it with TbSync.

https://addons.thunderbird.net/en-us/thunderbird/addon/tbsync/

https://addons.thunderbird.net/en-us/thunderbird/addon/dav-4-tbsync/

For some weeks Thunderbird Calendar won’t sync with Yahoo Calendar. I can’t seem to log into Yahoo Calendar from Thunderbird either. Every time I start Thunderbird I have to dismiss the Calendar attempts to log into Yahoo Calendar. Did something change or am I doing something wrong? I can’t get past

What apparently happened was some time near the end of the year 2020 Yahoo Calendar switched from the calDEV to the iCalendar (ICS) format. I had to get a new link and resubscribe to all my calendars.