Make it easy for us to block a certain email address.
Just one click done he or she is block from sending mail
Save time while browsing through your mailbox by clearing out the unwanted email. Yahoo Mail lets you anonymously add up to 1000 email address to your blocked list, or remove them if you change your mind. Here’s how: https://help.yahoo.com/kb/block-unblock-email-addresses-yahoo-mail-sln28140.html
C. R. commented
geez, it only takes 2 clicks. click the 3 dot icon next to the Spam button, then click the block senders choice. Oh, they COULD add a block sender icon on that menu bar too, but they probably won't as they don't care about making things easier/faster.