GeForce Experience error 0x0003, already reinstalled

Reinstalling rarely fixes that one because it's the Nvidia services, not the program. Open services.msc, find the Nvidia ones (Display Container, LocalSystem Container, Telemetry Container if you have it) and make sure they're running and set to automatic. Restart them, then restart the PC. If that does nothing, run netsh winsock reset in an admin command prompt and reboot. And honestly, Nvidia has replaced GeForce Experience with the Nvidia App now, switching to that might just make the error go away.