According to this documentation, Space admin should be able to configure the restricted page permissions in the Confluence, but unable to do so in the latest version of Confluence.:

https://confluence.atlassian.com/confcloud/permissions-and-restrictions-724765432.html

Page restrictions

Page restrictions work a little differently to global and space permissions. Pages are open to viewing or editing by default, but you can restrict either viewing or editing to certain users or groups if you need to.

Don't forget, every page in Confluence lives within a space, and space permissions allow the space admin to revoke permission to view content for the whole space. Even the ability to apply restrictions to pages is controlled by the 'restrict pages' space permission.

Steps to reproduce

1. Create a space that has a group able to administer it (in Confluence Cloud this defaults to "administrators").
2. Create a two users, Alice and Brianna, add both to the administrators group.
3. Log in as Alice, create a page in the space.
4. Add a restriction to the page so only Alice can edit or view it.
5. Log in as Brianna, visit the Restricted Pages section in Space Admin.

Expected results

Brianna can modify the page permissions because she's an administrator.

Actual results

Brianna can remove the "Only Alice can view/edit this page" permissions, but nothing else. She can't add herself or anyone else, which isn't helpful if the page needs to remain restricted but additional individuals or groups need access to it. Trying to view the Page Information page or the page itself gives a "No permission" message with a button to request access.