I can't find a way to report this as a free user without a support plan, but it looks like this feature is totally broken. My team imported an old Confluence self-hosted server database into the free Cloud plan, and it included some space permissions which we need to wipe out. This feature works on individual pages, but the feature to "Grant all users permissions for this space" constantly errors out even from accounts with full admin permissions. According to Chrome's inspector, the actual error is this:
java.lang.IllegalArgumentException: You are not allowed to add the SETPAGEPERMISSIONS permission to the anonymous user.
It seems like it should be a pretty easy fix on their side of things, since it looks like the blanket permissions are just being set in an invalid way, but I can't see a way around this from the user side. Does anyone know a way around this? Without being able to reset all of the permissions, my team is unable to work with this space.