Based on your description, I think that is what happened--your USB drive is being seen as a data drive, not a bootable drive. I'd look into that as a first step.
I discovered this YT video using RUFUS to create a Bootable USB - all’s well now...except for the Mint setup as I’m still working thru that part.
How to Create a Linux MInt Bootable USB on Windows (Using Rufus)
https://www.youtube.com/watch?v=kuqiFx13D0k&list=FLLR0KZJRLxO4vVbc4-lAyjw&index=1