Which setting do you have for Booting? is there a "LEGACY" option? You need to select that if there is. Disable secure boot if enabled.
What OS are you trying to boot from the USB? And how was it prepared?
You do understand that changing the bios type ie uefi to legacy or the other way around results in a no boot into windows. Most motherboard mfg have a quick or fast boot menu so you do not have to change anything in the bios [other than turn OFF fast boot IF it is enabled]
Since you have not provided any info on your system, it is basically impossible to help you.
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