You are correct; the "Experiences/Things to Do" section is typically an unpaid placement driven by Google's ecosystem partnerships, not direct SEO.
To appear there, you must integrate with one of Google's designated booking partners (e.g., Viator, GetYourGuide, or specific POS/booking software that feeds data to Google). Your GBP listing must be fully verified and use appropriate Schema Markup (like LocalBusiness and Event or Product) to clearly define your offerings. Google aggregates this structured, transactional data from these trusted sources to display the "Experiences" badge.