Board Thread:Support Requests - Getting Technical/@comment-33491589-20200517200952/@comment-9605025-20200517225127

That is not what Special:BlankPage is for. Sandboxes are not an actual feature. They are just pages that exist for the purpose of testing things. As far as the software is concerned, they are no different than any other article page. As such, there is no way to restrict editing/viewing to just yourself.