Right. Which is why there’s no science to back up the claim that marijuana causes schizophrenia.

Marijuana causing schizophrenia would be easy to determine if nobody was schizophrenic before the reefer. Before then they were just possessed by demons.

There's a big difference between a direct cause and a potential trigger for a condition with specific endogenous prerequisites.

Is it like a catalyst?

Sometimes, but not always. In chemistry, catalysts can help initiate or facilitate chemical reactions, but there is often another input required to kick start the process (e.g. heat).

We know that cannabis can act as a catalyst for schizophrenia, but we also know that not everyone who is predisposed to schizophrenia develops it 100% of the time after cannabis use. There are degrees of predisposition, and a bunch of other factors that contribute to this.

Does a freezer make ice, or does water make ice?

A trigger requires a gun to actually do anything.