Anonymous
It seems to me that you ended up with what you don’t want to have — mixed CSM & UEFI setup.
In Windows you can check it through Msinfo32.
If you are in UEFI mode, it’ll return something like: “Safe state”, “UEFI” and such; otherwise it’ll mention “Legacy” or “CSM”
In Linux you can check it through command efibootmgr.
If it returns UEFI boot variable, it’s booting in UEFI mode; otherwise, if it returns something like “EFI variables are not supported on this system”, you’re in “BIOS-mode”.