Facebook uses a Content Delivery Network (CDN). When a user changes their privacy settings, the CDN receives a command to restrict that specific URL.
Sometimes a user locks their profile after leaving it public for years. Google continuously crawls and archives public data. Go to Google Search. private facebook profile picture viewer top
Tools like mSpy and Eyezy are legitimate for parental control and employee monitoring, but they require physical installation on the target device with proper consent. Facebook uses a Content Delivery Network (CDN)