Welcome to Android Central! If you uninstall the last app that you installed, do the Settings work again? If so, it might be that particular app causing issues. Does the same problem occur if you install some other app to get the used space over 80 GB again?
Another possibility is a counterfeit phone. Use an app like CPU-Z and to find out which CPU is in the phone. It should be from Qualcomm or Samsung (depending on the variant). If it says Mediatek or something else, then it's a fake/knockoff.
02-11-2019 12:09 PM