this was how i first saw the new search box. In my mental model everything below the box are results. So the search button looked like it was another type of result. I think design guidelines should prevent this kind of situation.
From my intuition the search button should be on the right next to the search box. Instead there is this search reset button. I only recognized it exits just now.
To my surprise google is also like this. It also has this weird search reset button that I never realized existed. The difference is, that google at least clearly distinguishes the search button from the results.
I think discourse did many things right from a UX perspective. But there are also some odd things. Sometimes changes are an improvement and sometimes they are just changes.
I think the root cause for this is, that changes are done in an ad hoc manner without a design system that is based on clearly defined guidelines. It grew from the intuitive knowledge its creators acquired over the years. The paradigms behind the UI decisions are not clearly verbalized and are made in a quasi dictatorial fashion.