Lots of places in the help center (e.g. "How do I ask a good question?," "What types of questions should I avoid asking?," "What does it mean if a question is "closed" or "on hold?,"" etc.) point to "What topics can I ask about here?" but that is apparently empty set. There is not even a pointer to the on-topic tag on meta.
Lots of questions get closed, but how are askers (especially those who aren't already longtime users) supposed to know what they can ask about and what's off-topic? Why is this lack of guidance part of the site setup?