It turns out you can, but it's not intuitive. You can create an account, rate some books, then request a rec with all of the fields blank.

E1: Well, it worked the first time. Now the "AI Librarian" API call 403's out on me, according to my browser's web inspector.

E2: Oh, wait, you totally can do the "what to read after <X>" flow, you just have to click the "what to read after..." field in the top left.

This is the better URL to get there:https://whattoreadafter.xyz/

Hmmm, from the home page URL, I enter a book. I then click on the book, confirming that it's the one the app knows about.

It then shows me the same book, and a summary of it, and asks me if I want to read it.

Below that, it shows me a set of books in the "No Labels" category.

For all the books I've tried so far, it's given me this same set of books. House of Leaves is very different from A Time of Gifts, so it's unlikely that they're recommendations based on the book.

I haven't tried logging in, though.