It certainly seems to be the case that the theme is blocking the normal search, and there's not much I can do about that.
Switching theme to twentytwenty, the search does find the text from the checkboxes (I made a test listing post so I could be sure to check that).
That's the good news. The bad news is that the search powered by the View still fails to find such text (the same search as the standard search that works).
I'm taking a copy of your database so I can set up a site locally with the same, it will be easier for me to try and spot what it going on.
On my local copy of your site I created a new Listing with some content that I knew meant it should be returned by a particular test search, and then created a new View on a new page to test it, and it worked.
So I returned to look at your View, and noticed that the Query Filter section was missing a filter for the text search input: there is even a warning about that in the editor, see the screenshot.
After clicking that button, a filter for text search field was added (second screenshot).
My test posts didn't match the other filter criteria, but when I removed that other query filter then the text search performed as expected on the front-end, finding the content of the checkboxes fields.
Please try the same on your own site, you should find that it works after updating the query filters.