USB port not functionning anymore on Samsung Galaxy Tab S3i
If you have installed the app you have also tested the USB microscope, right? If yes most likely this broke your USB port physically. Also that the device does not charge correctly when powered off is a strong indicator that you are facing a hardware and not a software problem.

When the USB port does not work correctly this usually means that the soldering points are broken so that electrical power sometimes can pass the USB port, however it is way too less to charge the device (loose connection).

To fix this the device most be opened and the USB port have to be re-soldered, sometimes also the USB port have to be replaced.