@Garavar It's not just numbers but F1, F2, F3... button's in the keyboard. So, try to press thus keys when you want to edit copy files.

@mitu It worked! Thank you for helping me.

I've created a script in the RetroPie-Extra repo for adding the Pico8 as its own system to your RetroPie install: https://raw.githubusercontent.com/zerojay/RetroPie-Extra/master/scriptmodules/emulators/pico8.sh

I should mention...I did that for about 10 seconds before realizing vfat sucks and committing the drive to ext4. Same principle though.