Here is a topic that I like a lot because I think that many people underestimate its importance. I do think that some themes aren’t well-coded and will never rank as good as they should.
Google has an above-the-fold penalty. It means that when there is no text at the top of the website, the website is penalized by Google. However, today, there are many themes with huge sliders or pictures at the top of the theme. I do think those themes will never rank well. The new trend of theme author is to add huge pictures at the top of articles before or after titles. It is a really bad behavior. I think that Google may see those pictures as being meaningless.
Too many links
Some themes use 3 links for a snippet of a post or page. There is one link for the picture, one link for the title of the post, one link for the excerpt. Those 3 links point to the same post or pages. This is a google leakage. In the initial version of
On an article, the author may decide to put a link behind the author name, the date. The author may also add a link behind the category. Compare the links that can be found on a theme and the link that you can find on your favorite website. you will see that popular websites have much fewer links
Google hates hidden links and when you use in the CSS code: “display:none”, this is really dangerous because the website can be banned because of it. Then, sometimes, some fonts can be hidden when the background color is equal or nearly equal to the text color.
Some wordpress themes don’t deliver the same content to GoogleBot and a user. In this case, it ends up in a proper google penalty. To avoid this problem, visit google search console, and check if the website appears to be the same for googlebot and the user.