Veganism? No.
AI? No. (*a few glances exchanged in the audience, but no actual applause*)
Dianetics? No.
Geography? No.
Geology? In some sense maybe Yes, but that's unlikely to be helpful.
Related to Art? No.

Astronomical? No.
Creationism? No.

One of the nine billion names of god? No.

We know that this is an ISM and refers to to something that was invented by humans, and that's about as far as we've got.
We do know that it doesn't begin or end with p, c, or anti. It has nothing to do with geography, geology, art, literature, or astronomy. It's not veganism, idealism, creationism, or dianetics, nor is it named after a person. There is a possible tenuous link to religion/spirituality, although all the guesses so far have not led anywhere. Normal people will think that the AOTC is crazy, those with more specialised knowledge will think that it doesn't work, although it still has its supporters.

Recap. Mostly correct, although you only know that it doesn’t begin with C or end with P. I struggled with my answer to “invented by humans?”, so I’ll attempt a clarification. If we think of, say, a continuum of isms from Marxism (clearly invented by humans) to magnetism (clearly not), I think this is a bit closer to Marxism. But it is something that humans have thought of that could conceivably be fact—and if it were fact, it would be more like magnetism.
Economics? No.
Aliens? No.
Contain the name of a being? No. (Well, technically yes, but that’s essentially coincidental).
Politics? No.

Hypnotism? No. On the Marx-Magnet scale, the AOTC is to the right of hypnotism.

One more clarification. B’s recap stated “those with more specialised knowledge will think that [the AOTC] doesn’t work”. I’d say,rather, that they’d think it isn’t true.

1.6 billion? I think that the adjacent spiritual/religious concept quite probably has more than that number of adherents. The AOTC is a more technical notion (and term), which would be unfamiliar to (most of?) those adherents. I think. The adjacent spiritual/religion-adjacent concept might be a helpful route to the answer.
Governmental? No.
Associated with a particular group? For the AOTC itself, I'd say No. But the adjacent spiritual/religion-adjacent concept is certainly associated with various identified groups.

Presumably not, since you wouldn't have described it as spiritual...

Spiritualism? No.
Dowsing? No.

Corporeal? The best and least misleading answer is No. (There is a pedantic sense in which the answer is Yes, because “anything to do with” is pretty broad and vague.)

Solipsism? No—but the audience awakes from its torpor and there is *some applause, mixed with a little laughter* .

On my Marx-Magnet scale^©, I'd probably put the various isms that have been suggested in the following order, with Idealism/Solipsism/AOTC being fairly close to each other. All three are invented by humans but could in some sense be fact.

Marxism ... Veganism ... Hypnotism ... Spiritualism ... Creationism/Btheism ... Idealism/Solipsism/AOTC ... ... Magnetism

Idea about the nature of the entire universe? Yes! *sustained applause*
To do with logic? No.
Relate to death? The best answer is No, though an indirect argument could be made for Yes.

University Philosophy? I'm not an expert in university philosophy curricula, but I'll speculate as follows: the AOTC would show up somewhere in the curriculum but is unlikely to make an appearance in an Introduction to Philosophy subject. The AOTC has an entry in the Internet Encyclopedia of Philosophy, the Stanford Encyclopedia of Philosophy, and Britannica.
Plato's cave? No.
Has anyone said Existentialism yet? No.
Is Existentialism the AOTC? No. (I'd put that more in the vicinity of Spiritualism on the M-m scale.)
Does it entail a belief in predestination? You just had to ask that, didn't you? No.