[Solved] DELL Inspiron 15-3521 - BOOT with USB on Legacy does not work

My Dell Inspiron 15-3521 than how it can not start with BOOT USB I have 3 different pendrive which on other laptops or PCs run without a problem and on Dell as I plug in a pendrive with BOOT it freezes the screen and does not go. When I hook up to the micro SD card reader through the adapter, again after pressing F12 I do not see it on the BOOT list. Does Dell in its bios by default somehow blocks BOOT after USB LEGACY?
Is the only option in the Boot UEFI settings to use the Ad Boot Option and add there Boot for USB storage prepared for the MBR partitioning scheme for UEFI computers?



Or maybe it can be somehow unlocked in the bios or enter into some advanced bios mode if it exists.

As far as I remember, there are such things as "Legacy ROM support" or "Legacy boot support". Because when turned on, legacy sees a pendrive but I will not boot from it. There is one other option somewhere in the BIOS. I don't have Dell at hand, I won't tell you exactly.

You can still have the security boot option which you must give disabled before giving enabled to legacy boot. (because it becomes gray after unlocking legacy)

Pendrive try to do as MBR for BIOS, check if it works in another computer.

In my dell it probably helped to switch something from disk, AHCI / ATA ??
It was also slow, but it was possible to install seven.

However, the carriers were made without MBR partitioning for UEFI computers, everything changed after the change. Probably in a different form Dell did not accept data carriers.