Hi. My name is***** you for your question and the opportunity to assist.
Yahoo is blocking the Windows 10 mail app.
Close the Windows 10 mail app.
On the Yahoo page, click your name and select Account Info.
on the left click Account Security.
Enter your password ***** requested.
On the Account Security page go to the bottom and move the slider
for Allow Apps that use less secure sign-in, such that it turns blue to turn it on.
Re-open the Windows 10 mail app and your email should start coming in.
Let me know the result please.