Funny, it works just fine after all updates on my iMac. And my iPad. And my iPhone 😉
Hint, hint, hint... 😁
Your operating system has nothing to do with Yahoo Mail. It is web based.
Fix problems with New Mail: https://help.yahoo.com/kb/sln28075.html
Windows 10 is unlikely to affect Yahoo mail, but just in case, try it on a different machine, or on your phone.