HP ProOne 400 G2 Legacy boot option unlock

I have HP ProOne 400 G2. And I need to unlock legacy boot option to boot from Lumix usb to install it. Maybe I am rong but I think that there's is UEFI only. I ask HP forum to help but they answer me they do not support Linux and I can not boot from it and I can not install it (why?) and even if I install it (what?)... I do not know which BIOS provider is it. If I insert legacy bootable Lunix usb its just skip it and boot from internal preinstalled Windows 10. Please advice me to install Linux on it.
BIOS located there https://support.hp.com/us-en/drivers/sel...ku=T4R03EA

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