I just tested via your back-end but no matter what I typed in, I could only see page results from the “Offer” category or items which are uncategorized.
I guess the problem is that uncategorized items are also appearing? If so, I've turned off the Show posts/CPM with empty taxonomy terms? option on the Frontend search settings -> Advanced panel, they should not appear now: https://i.imgur.com/GurTDzj.pngBest,
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