There's like a 500 pages rulebook, but yes, if you're applying for a .genericterm, you have to make it available for purchase. Or in ICANN's terms, "closed generics" are prohibited.

Really? I’ve had my eye on a domain with a tld that a registry owns but does not make publicly available for purchase. It’s been that way since 2015. Amazon owns it. I guess if such a rule exists it’s a new rule, unfortunately.

Seems like this is the case for a few domains. .book, .author, and others got bought by Amazon who hasn’t really done anything with them?