Hi all!
Im replying to this old post because I too had the issue of Ultra Fast boot and couldn't get into BIOS easily.
The solution above with Windows 10 Recovery boot, wasn't presenting the UEFI option for me so I couldn't get into BIOS that way.
However I found another nifty solution to disable Ultra Fast Boot!
Install Gigabytes APP Center + Fast Boot software. From there I could either boot into BIOS or just set the Boot type back to Normal or Fast Boot which solved my issue!