I've checked the search instance configuration, everything was actually correctly configured there. I did some debugging and I found that the problem was with the Index table configuration. The content indexing was turned on, but you only needed titles, categories and tags: https://i.imgur.com/n5dUyEI.png
I have turned off that option, and re-created the index table for you. Now it should return only relevant matches based on title or categories or tags, ordered ascending by post title.
I hope this helps!Best,
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