Getting the Bitlocker Recovery screen was an interesting change, but it didn't have any lasting effect. It was cleared, and everything worked normally, when I reset the PC and booted from my hard drive. According to this, an MBR drive can be booted on both legacy and UEFI systems as long as they're configured correctly, and MakeDisk apparently does so: https://unix.stackexchange.com/a/699894 "No, that part of the spec only says The boot code on the MBR is not executed by UEFI firmware which means the the 446-byte region in the MBR containing the binary instructions for booting the system won't be run in UEFI mode. It's still possible to boot from an MBR disk in UEFI mode if you create a proper ESP (EFI System Partition) on it. UEFI systems only boot executable images in the ESP. So by putting a proper BIOS boot loader in the MBR and a UEFI boot loader in the ESP you can have a disk that boots in either mode" A lot of conflicting information came up when I googled this, but this matches my experience, so I'll go with it. I still don't understand what 3.64 and 4.06 MakeDisk are doing differently in the "Multi-Partition UEFI GPT" case, where the 3.64 USB was able to boot on my Windows 10 system, while the 4.06 version goes to Bitlocker Recovery. However, as long as MBR mode works in both cases, I guess that's good enough.
