Hi there, from my experience, I would say a virus is the final factor for you to take into consideration. As you find there is no file on the USB drive even your computer can recognize it, I guess the files are set to hidden or lost. You can try to unhide these files on the drive on your computer or utilize data recovery software to scan for lost files.
Based on your computer, the ways to unhide files are quite different, we have articles for you to unhide them on Mac here: Make Mac Show Hidden Files on Sonoma, Ventura, or Earlier
For Windows users, you can read this article since the way to show hidden files from a USB drive or an SD card is similar: 6 Ways to Unhide or Recover Hidden Files on an SD Card
If unhiding files fails to make the files accessible, give iBoysoft Data Recovery Software a chance, which can recover deleted, lost, or accessible files from any external hard drive!