I use a USB 2.0 stick in a USB 2.0 port.
You can use the FlashBack Button (also with an FAT32 USB 2.0 stick) BUT it is harder to tell if it's working and when it finished.
And sadly that can lead to some people turning off the PC (via the PSU switch) or pulling the USB stick out too early.
And then they have a Bad BIOS flash that may or may not be recoverable.
Here is a good guide if you do want to use the FlashBack Button:
[Motherboard] How to use USB BIOS FlashBack™? | Official Support | ASUS Global
(Notice that the FlashBack port is a USB 2.0 port and that they explicitly state to format the USB stick as FAT32.
EZFlash has a progress bar so you know exactly what is going on.
But either way be patient because it is a fairly slow process.