On the topic of AI, PLCs are definitely 100% NOT AI. It is pre-defined logic, cast in stone. It can be simple (like a roller-coaster) or complex (like a flight control system), but always designed to be deterministic. Where it cannot be deterministic is shuts down or goes into fail-safe. Often there are multiple controllers, and/or replicated controllers for redundancy/confirmation. Replicated PLCs may have different physical inputs testing the same conditions, and in extreme cases may be independently developed.
As for AI, a lot to date has been generative heuristics (e.g. AlphaGo Zero) or large-language model (LLMs, e.g. ChatGPT). The benefit of PLCs is that you can formally (mathematically) prove it, which is not possible with AI.