Sam2 -“Health: The Gemara says that “Kol Leitzanusa Assura L’vad Me’avodah Zarah”. It doesn’t say Kefira, just Avodah Zarah.”
Kefira is a type of Avodah Zara! There are many proofs -I’ll just give you one. In Mitzrayim it says Pharoh considered himself a diety. This is AZ. It also says “Mee Hashem Asher Eshmah Lo?” or something like this. Kefira was the root of the AZ there.