Other then legacy and uefi does it have a CSM compatibility support mode? An option to enable usb initialisation before bios? Eg wait for usb initialisation?
Some “boot faster” options kind of reorder boot initialisation to a point where it’s not holding the system back.
Though I’m really running out of suggestions… I can imagine you’re pretty frustrated. I know my Dell laptop was a pain to get the right settings to get usb to boot and the stupid 100db beep to silent on boot interruption.