This may not help, but there is a setting in config editor - mailnews.tcptimeout - that allows changing the servertime out in seconds.

David: This did not solve my problem. I have version 91.5.1 Thunderbird and it's not connecting to their server so I can send and receive emails. I'm thinking of just reinstalling the program altogether unless I get more answers from the community if they're having the same issue or know how to fix it. Thanks for your help anyways. Claudia

I am not close to Yahoo, but you may need an APP password, and OAUTH2 authorization may be a player here. Reinstalling rarely fixes this, but miracles happen. Good luck.

This is how I got TB to work again. I changed two of the server settings temporarily to see if I could get a connection. Under Account Settings / Server Settings / I changed the server name setting to "pop.mail.yahoo.com" and the port to 995. I closed TB window and opened it again to see if I could get a connection. Nothing cleared up. I changed back to the default settings to "imap.mail.yahoo.com and the port to 933". I closed out of the window again and opened it and everything started working. I got all my emails to open up. I can now send and receive emails again after 5 days of TB being down. This tinkering around worked for me.