When you install Windows using a Legacy Device is marks the Boot Volume with an Master Boot Record (MBR) label
I use easybcd to load all my ISO’s on a single USB which doesn’t support UEFI
You need GUID Partition Table (GPT) for UEFI Boot
You can check this via Disk Management
Restart the PC into Safemode with Command Prompt ( Or Hold down Shift when you click on Restart on the login screen )
*You will need Local Admin password for this!
Run this command to make sure the drive can support GPT
Then Run this
After this you need to change the Boot Loader to use UEFI instead of Legacy
To do this with a System with Bitlocker
Suspend Bitlocker before hand then reboot in command prompt
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