You can make these changes globally or at a project level. At both levels, the navigation path is the same: Administration > General Settings > Analysis Scope .
Although we can see the General Settings > Analysis Scope at project level we do not see it within the Administration tab when viewing all projects (SonarCloud)
I’m the administrator for the organisation and so I don’t think it’s related to permissions.
Sorry for the late response.
It’s currently not possible to define settings at organization level. (the page doc you linked is about SonarQube, not SonarCloud).
You can track progress on this feature by following/voting SCCOMM-2.