How do I create an app-specific password for iCloud?
Solution 1:
The missing information was provided by @GordonDavisson (and if he wants to post an answer I will accept his instead of mine):
To generate and use app-specific passwords, your Apple ID must be protected with two-factor authentication.
This is actually on the Apple Help page, but oddly not included in the section "How to generate an app-specific password" (even though it was the missing step for exactly that question) but instead buried between an explanation of what an app-specific password is (which was of no value to me) and fine print about different OS versions. I used the headers to skip right to the relevant information (which is what headers are generally for) and didn't guess that a critical piece of information would be placed elsewhere.
Solution 2:
It does exist, exactly where the not-outdated-at-all help information says it is.
The support article you link says:
Sign in to your Apple ID account page. In the Security section, click Generate Password below App-Specific Passwords. Follow the steps on your screen. After you generate your app-specific password, enter or paste it into the password field of the app as you would normally.
Doing this leads you to a page that looks like this:
And there you can create all the app-specific passwords you like.