How do I tell my uncle, an AlAnon believer, that I no longer want to affiliate with him?

The other night, I was trying to go to sleep when I overheard a telephone conversation between my aunt and my mother. (The phone downstairs is right next to the opening of a vent which is connected to another vent in the attic, AKA my bedroom, so the sound carries right through.)

My aunt was talking about how her husband, or my uncle (in case you are so daft as to not be able to make that connection yourself), was getting “very serious about AlAnon” and was even considering trying to get his friend in on it.

I guess my uncle went too far down the alt-right rabbit hole. I’m supposed to go downtown to play some games of backgammon with him next weekend, but I don’t want to be affiliated with a believer in AlAnon nonsense.

He just texted me the backgammon emoji and said “r u ready for Friday?” How do I respond in a way that makes clear that so long as he is in that cult I will not be doing anything with him?