To me, this looks like a Yahoo problem. In doing a web search, I see this question has been posted on many websites with other email clients. I was easily able to duplicate the problem.

Is this the "Edge" problem? If not, then what?

This is possible overreaction by me, as multiple Yahoo problems were reported together. If the OP did not see an error message with word 'EDGE: ' in it, my response may have been incorrect. Thanks for seeing this, Wayne.

I was successful by creating app password at yahoo.com and setting authentication to 'normal password' . See if that works for you