Don’t format the USB yet. What’s happened is your SanDisk’s file system (the part that tells Windows how to read your data) has gone corrupt, which is why Windows is calling it “RAW.
Try Stellar Photo Recovery software to recover your photos from it. The tool can help you with the drive that turned RAW. Once you’ve safely recovered your stuff, then you can format the USB (exFAT is a good option if you use both Windows and Mac) and start using it again.
