That is still correct.
Howerver it's not quite as simple as saying that candidate isn't supported - explicit write to candidate is indeed not supported but as is stated in chapter 21
The REST API in the UG:
The server hides all NETCONF datastore details for edit operations, such as the :candidate and :startup capabilities. When a client writes to this resource, the server performs the edits in the datastores used; if the candidate is enabled, the changes are written to the candidate, and then the candidate is committed; if the startup is enabled, the changes are written to running and running is copied to startup.
Similar words can also be found in section
1.4 Coexistence with NETCONF in RFC 8040 (RESTCONF Protocol).