not sure if this will help you but there is a neat website that allows you to build free maps for older Garmin models that didn't have them at first like Fenix5
1990s is going way back though, they didn't even have mass-storage mode then, it was their proprietary "garmin mode" for usb which only things like BaseCamp can talk to
oh bud, mine doesn't even mention USB in the manual. I got the thing for like a dollar at goodwill haha