To format the drive in Windows 10 as a GPT disk:

Right click on "This PC" and select Manage In the Computer Management window, select Disk Management toward the bottom of the left side If a message appears asking if you want to initialize the disk, you can do so and select GPT and click OK If the disk already has a format, you can right click under where is says Disk # and there should be an option to "Convert to GPT Disk"
NOTE: This will erase anything you have on the disk currently. After the disk is set to GPT, you can right click the unallocated area (should be the whole disk) and choose "Create a New Simple Volume" Set the file system type and label if desired, this will format the drive

@Shira See https://retropie.org.uk/docs/Running-ROMs-from-a-USB-drive/#configure-fstab-to-automatically-mount-usb-drive for more information about permanent mounts via /etc/fstab.

@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.