How to mark over 17 thousand email messages read at once

I have over 17,000 unread email messages in my Yahoo Mail inbox.

I tried to set all them as read by selecting Select All and then More → Mark as read (keyboard shortcut K) but it only marks less than a hundred every time. I want all of them to be marked as read at once. How can I do this?

I also tried searching using is:unread and then did the above procedure, but it did not seem to mark any messages as read in this case.

I am using the modern Yahoo Mail theme, not the classic one.