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/