Glad you mentioned windows version...my laptop is Win11 Home. Hubby's computer is Win10 Home. So there may be a combo of Microsoft, ATT, and Yahoo not playing well over WiFi (in my case). Did I mention that my internet is ATT fiber to the house router?
What URL are you using to log into for your sbcglobal.net email account? I've seen several different ones. Yesterday, I went to my 2nd Win10 computer that has Ethernet connection to the router (not WiFi). I used my bookmarked URL to login using Firefox (http://my.yahoo.com/) and got the standard error message we've all been getting. I've used that link to log into my sbcglobal.net email account for MANY years. I tried DuckDuckGo, again with no success.
Last night, I was sitting at my regular laptop (Win11 WiFi Firefox) searching my old files. I found an old URL that I first used in 2011 and last changed the password in 2022. That URL was (https://login.yahoo.com/). Last night I logged in using that URL and selected "Keep Me Logged In". I was logged in with no problems and when I started my laptop this morning, my sbcglobal.net email was up and waiting for me to read my messages. The only difference between this "event" and when I first posted--is the URL I used to log into.