For the most part, brands do not have the ability to turn off or disable the Q&A section on their GMB listing as there is no option via the GMB interface, API control or from requesting to Google Support to turn off this section for a specific listing.

However, the one exception to this is if that listing begins to get bombarded with demeaning/irrelevant comments from users due to a public media incident. In scenarios such as this, you can then reach out to Google's Support to have them both disable that section and remove such content.

Fortunately, Google has recently expanded the API tool set (v4.5 release) to make it easier for platforms like LocalClarity to give businesses the tools to be notified instantly of new questions.
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The following thread on the GMB Support Board goes into detail as to how challenging it is to have people post content that isn't really a question, while others actively answer questions despite having no knowledge of the business or even the subject.  https://support.google.com/business/thread/1857391?hl=en
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