I got my Cox email address working with the imap.mail.yahoo.com server in eM Client.
I received the following emails about the transition.
* Your Cox email account is gearing up for a move to Yahoo, Elsie (from Cox) (sent in March)
* The countdown to Yahoo Mail has begun (from Cox) (sent in April)
* Almost time for your Cox email to move to Yahoo! (from Cox) (sent in May)
* Important information about your Cox account (from Yahoo Mail) (sent in June)
The last email gave me clear instructions on how to proceed.
I didn't have to generate an app password.