I need to decide whether it is more straightforward to create a bootable Ubuntu drive in UEFI or standard BIOS. I do not want to create or install it through any more ambiguous route than necessary because I have experience with accidentally installing one on the other's environment.
Open the System Information Utility (Win Key + "R" > "msinfo32" > OK)
In system summary, look for "BIOS MODE".
Alternatively, check Disk manager. If you have a partition on your disk for "EFI system partition" then you are using UEFI. If you only have system reserved and C:, its probably BIOS.
Hope one of these helps
You can also use Windows Panther directory logs:
type C:\Windows\Panther\setupact.log|find /i "Detected boot environment"
Extracted from: http://www.sysadmit.com/2017/04/windows-uefi-o-legacy-bios.html