If the restricted section does not need to be part of the page you might try the include plugin, see
https://www.dokuwiki.org/plugin:include.
What I mean is have a "main page" accessible to all, and include the section which is a page on it's own. You can set different permissions for the "section page". The include plugin should respect the ACL so the section is only included in the "main page" if the user has permission to view/read the "section page".
Might work but not very comfortable to handle.