@AndersHP check out Mounty. I use it for the Mac a lot of time and seems to work really well. https://mounty.app/ hope this will help you!

@Parabolaralus Yeah I'll either figure it out or install linux (what is a good distro for dell laptops?). This pc I found at a garbage dump, the hard drive was failing, the battery shot, and it was a little beaten up from being discarded. I restored it with a ssd, and a new battery. I think it came with windows 7, but there was no sticker on the back. I downloaded the USB Windows 10 upgrade from microsoft, these were free upgrades some time ago. I had assumed Education postulating that it would activate for free, but I have no qualifications for those terms. Back on topic: ExFat has been working great with allocation unit size 8192b. NTFS-3g may have been a problem in particular with dosbox because of the write syncs.

@zerojay Thank you!

Why didn't you install RetroPie on the PiDrive? All you need to do is install BerryBoot on the SD card, add the retropie image to the USB drive and install it via BerryBoot.