I have a 2019 ThinkPad X390 with Windows 10 and want to install Ubuntu. I have always used Legacy Boot previously, not UEFI, and want to see how to have that option. In the UEFI-BIOS, I can see that the option to change
UEFI/Legacy Boot from
UEFI Only to `Legacy Only' is not selectable and beside it is written the text
Unselectable for Kernel DMA Protection
How can the option to change this be enabled?