Are questions about authors on-topic, or just their works? For example, asking about authors' lives, motivations, interviews, or anything relating to their work.
I would say that they would be on-topic, but only insofar as they relate to an author's literary life.
We had a similar issue on History of Science and Mathematics early on. Would a question about Einstein's favorite style of eggs be on-topic? Obviously not, because, as far as we know, eggs did not have any role in Einstein's scientific work. Extrapolating that here, I don't think that a question about J. R. R. Tolkien's favorite sandwich should be on-topic, but I do think that a question about whether certain portions of his books related to certain events in his life should be on-topic.
Counterpoint: They should be on-topic. How do we predetermine whether or not a particular biographical detail is relevant to a writer's work?
For example, if someone asks a question such as this:
Was writer Foo fond of lollipops? The city Bar where he spent some time during the summer holidays when he was a schoolboy is famous for lollipops.
... it might at first blush seem like a trivial detail that has nothing to do with Foo's work and so a candidate for closure. But a priori we can't tell. An expert on Foo might be able to draw connections between lollipops and some of Foo's work. Perhaps a schoolboy character in one of Foo's plays is depicted as being overly fond of lollipops. Or perhaps a weird edible currency he says is used on a distant planet in one of his fantasy novels suddenly becomes less weird when we realize that this currency is based on the lollipops of Bar.
Even if such connections aren't already known, some future scholar might draw them. Or some unpublished manuscript of Foo's might turn out to be all about Bar lollipops. Absence of evidence is not evidence of absence—just because the relevance of this detail is not known yet, it doesn't mean that there is no relevance.
History of Science and Mathematics may have decided such details are irrelevant for their purposes, but it doesn't follow that they are irrelevant for ours as well.
I'm not claiming this is a good question. It is a bad one. I'm claiming, however, that it can't be judged as off-topic. To become a good question, it does need to be related to the work somehow, rather than staying at the level of biographical detail. But I think it could easily be recast as a good, indisputably on-topic question:
Writer Foo spent some time in city Bar during summer holidays as a schoolboy. Bar is famous for its lollipops. Do any of his surviving letters from his schooldays or later mention Bar or its lollipops? Do the city and/or lollipops figure in Foo's work? For example, is there a character in any of his stories that is inordinately fond of lollipops, or detests them?
And an enterprising answer might say:
Foo's poem Baz was written shortly after he was diagnosed with Type 2 diabetes. The following lines are often said to be about the eyes of his lost love. But in the light of this detail about his schooldays, they can be interpreted as a hankering after the lollipopular pleasures of his childhood: "Barred now from the sweet, bright orbs / that delighted my heart in days gone by."
You never know.