Key quote because my linked article is quite extensive:
> What the firmware will actually do when trying to boot in this way is reasonably simple. The firmware will look through each EFI system partition on the disk in the order they exist on the disk. Within the ESP, it will look for a file with a specific name and location. On an x86-64 PC, it will look for the file \EFI\BOOT\BOOTx64.EFI. What it actually looks for is \EFI\BOOT\BOOT{machine type short-name}.EFI - 'x64' is the "machine type short-name" for x86-64 PCs. The other possibilities are BOOTIA32.EFI (x86-32), BOOTIA64.EFI (Itanium), BOOTARM.EFI (AArch32 - that is, 32-bit ARM) and BOOTAA64.EFI (AArch64 - that is, 64-bit ARM). It will then execute the first qualifying file it finds (obviously, the file needs to be in the executable format defined in the UEFI specification).
> What the firmware will actually do when trying to boot in this way is reasonably simple. The firmware will look through each EFI system partition on the disk in the order they exist on the disk. Within the ESP, it will look for a file with a specific name and location. On an x86-64 PC, it will look for the file \EFI\BOOT\BOOTx64.EFI. What it actually looks for is \EFI\BOOT\BOOT{machine type short-name}.EFI - 'x64' is the "machine type short-name" for x86-64 PCs. The other possibilities are BOOTIA32.EFI (x86-32), BOOTIA64.EFI (Itanium), BOOTARM.EFI (AArch32 - that is, 32-bit ARM) and BOOTAA64.EFI (AArch64 - that is, 64-bit ARM). It will then execute the first qualifying file it finds (obviously, the file needs to be in the executable format defined in the UEFI specification).