‘The new BIOS setting does not completely support the boot device’ is among the most frustrating issues you may encounter on the Windows 10 PC. The issue might be a booting issue or even related to the external HDD. If you want to fix the issue, then this post might be useful for you. https://mcafee-activate-en.com/fix-the-current-bios-setting-do-not-fully-support-boot-device/