USB Boot Hidden

Hi,
I have an Inspiron 14 7460 and I'm trying to reinstall Linux UBUNTU 20.04 from USB drive but the USB Boot option doesn't appear on F12 screen. I already installed (so it's not a problem on USB).

The weirdest thing is the options selected on BIOS don't match with the options showed on F12 screen. I already tried to select the UEFI option and the Legacy Option too, but on the F12 part, they show the same options (Diskette Drive, Internal HDD and Onboard NIC for Legacy) and that options don't change even if I change the BIOS options (the Diskette option unselected, for example). I already tried a lot of tutorials and I don't know what to do anymore.