Is it more correct to say the ancient Maya or Mayans? Are you visiting a Maya or a Mayan site? Is it Maya or Mayas?
In the English tradition of Maya studies there is the preference of using the adjective Mayan with reference to the language or languages, whereas “Maya” is used when referring to people, places, culture etc, without distinction between singular or plural.
Even if it is not a rigid rule, this convention is the most widespread among Mayanists, scholars who study and write about the Maya. This distinction arose in the field of linguistics, where the "Mayan" adjective started to be used to define the linguistic family that incorporates the different dialects spoken by the Maya people.
For this reason, at least in specialized sources written in English, you will find the term “Mayan” limited to the languages spoken by the Maya people and "Maya" in the other cases. However, the use of Maya in search engines is a problem: googling the term “Maya” presents results including the 3D animated software and Maya Angelou, while if you enter “Mayan” the search engine gives you “Maya civilization”…