I recently got my old Dell dual-booting windows 10 and mint. Didn’t have issues getting mint installed (I used Etcher to burn the ISO to a USB drive), but windows absolutely didn’t want to play nice with Grub, and I had to use bcdedit to get it to load the boot menu. Working fine now, though! Looking at some articles, it seems like f10 is probably your bios key. It really ought to be able to boot from usb; my mobo is 12 years old and supports it.