I'm glad to help you, here are some solutions you can try.
- Adjust your settings. Finder > Settings > Sidebar > Turn on External Disks.
- Reboot your Mac then reconnect the USB.
- Force your USB in the Activity Monitor.
- Check your Mac software update. Apple menu > System Settings > General > Software Update.
- Reset the NVRAM/PRAM. Shut down your Mac, then press the keys Command, Option, R, and P for 20 seconds until you see the Apple logo.
- If these can't help you, maybe you should consider a new USB to replace it.
