In Salesforce, access to reports and dashboards is determined by the folder in which they are stored. If a dashboard is in a shared folder, anyone with access to that folder can view it. To "temporarily remove" a specific dashboard from public view without affecting the rest of the folder's contents, the Platform Administrator should edit the dashboard's properties and move it to a private dashboards folder (such as "My Private Dashboards"). Once moved, only the administrator (and those with high-level "View All Data" permissions) can see it while the changes are being made. Removing view access to the shared folder (Option A) would hide all dashboards in that folder, which is not the goal. Permission sets (Option C) control functional access (the ability to create or edit dashboards) but not individual record/dashboard visibility.
Private groups (Option D) are for Chatter collaboration, not for managing dashboard folder security.