The catalogs are still lists, so you can still reach them by
/lists/getbytitle(). But you do have to know the "title", which may not be what is in the URL.
For instance the URL to the Composed Looks catalog is:
But the "title" of that list is actually "Composed Looks", not "design", so you can reach it through the endpoint:
Edit to add: just did a quick check, in your example you used the User Information List (
/_catalogs/users). The title of that list is "User Information List", so it can be reached at the endpoint
https://server-url/sites/mysite/_api/web/lists/getbytitle('User Information List')/items
however, if what you want to do is work with user data, I would highly recommend using an endpoint designed to work with user data like
rather than trying to manipulate the User Information list directly.