The USB flash drive not showing in Finder could relate to the connection, Finder settings, etc., and the original file can't be found error happens when you are attempting to open a corrupted, removed, disconnected, or redirected file. Thus, it seems that your USB sticks are not stably connected.
A connected USB flash drive should appear on the desktop or in Finder where you can access the files stored on it. However, the USB flash drive is not showing up on Mac desktop and Finder, you should first check it in Disk Utility, the built-in disk management tool. It should display all recognized internal and external disks.
- Head to Finder > Applications > Utilities and open Disk Utility.
- Click the View button and choose Show All Devices.
- Check whether the connected USB sticks are listed on the left sidebar.
If you can't see the USB sticks in Disk Utility, it seems that macOS fails to recognize the USB flash drive, you can try to restart your Mac, check the connections such as the USB port, USB cable, USB hub, update the USB driver, and reset SMC.
If the USB sticks show up in Disk Utility, but it doesn't appear on the desktop or in Finder, you should change the Finder's settings to make them visible to let you access the data, here is how:
- Click anywhere on the Mac desktop and click Finder in the menu bar.
- Choose Settings to get into Finder's preferences.
- Select the General tab and check the box of External disks to show them on the desktop.
- Select the Sidebar tab and tick External disks under Locations to show them in Finder's sidebar.
Badly, the USB sticks are also inaccessible after trying the above methods, it is possibly damaged/corrupted, try to repair the USB flash drive with Disk Utility's First Aid feature, recover data from it with iBoysoft Data Recovery, and reformat it to make it usable again.