I have a USB that I saved files on but it is now undetectable. I have tried the USB on 2 windows computers and 2 Macs, and each time nothing appears in File Explorer and no sound of recognition of anything being inserted into the USB drive. I have downloaded the Recuva program but it requires a location to be indicated...and since the USB is not being recognised, there is no external location (only local disk, as on screenshot attached). Can you please help?
Recuva will not be able to work in this situation, as it requires that the drive be accessible in Windows and mounted with a drive letter.
Unfortunately, given that you're not getting any sort of reaction from it on four different computers, that sounds very much like the drive itself has failed. Most likely, the only feasible option for getting data off of this drive will be to take it to/send it into a proper data recovery service.