en.wikipedia.org/wiki/Mon_people

This claim is incorrect because UNESCO’s own official listings for the relevant countries do not recognize these games as UNESCO intangible cultural heritage.

On UNESCO’s official Thailand country page for "Lists and Nominations," the Intangible Cultural Heritage entries are only: Kebaya, Khon, Nora, Nuad Thai, Songkran in Thailand, and Tomyum Kung. There is no listing for Len Saba, Lor Kon Krok, or Mon Son Pa.

On UNESCO’s official Myanmar intangible cultural heritage page, the country has 1 elements inscribed: Myanmar traditional New Year Atā Thingyan festival. Again, these games do not appear there.

UNESCO’s FAQ also explains the distinction between UNESCO-inscribed elements and national inventories. It states that "At the national level, States can register what they consider appropriate for their inventories without intervention from UNESCO." So a practice can be part of a national or local heritage inventory without being a UNESCO-recognized element.

That means the sentence overstates the status of these games: even if they are documented locally or nationally, the available UNESCO records do not show them as UNESCO-recognized intangible cultural heritage.