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Fast answer is click on the face and scroll down. Not sure if you really have to scroll, yoast design was changing last weeks. But you will find it if you click the face. Ok that should answer everything, because Yoast shows you what it means you are not doing or not doing good enough.  And what todo exactly! For both KW-Optimization and Readability. Special for readability is, you can click on an eye-Icon wicht shows you the sentence where you are doing wrong in a colored mark-up. But, to see this, you cant be in most Pagebuilders, you have to be in the WP-Editor mode, so for some Pagebuilders  eg Elementor you need to go to WP-Editor. to see what yoast is saying. And for some other pagebuilders, yoast sometimes don't see the text and dont know if it is optimized. But in this case the face would be red I guess.