Yes you can jump straight to F21.
Yes, updating BIOS/UEFI this way is more or less the same as flashing. If you select this update, GCC will restart your computer (or ask you to doit, can't remember), then it will boot to BIOS/UEFI update and caution you not to turn off the pc or press any keys. After some 20-30 seconds, the BIOS update will be completed, the PC will restart and you can enter BIOS to set or reset settings, or boot to Windows normally.
GCC likes to treat BIOS/UEFI updates as if they were regular driver updates. Yes, it is a little bit safer if GCC automates the process but it is still wise not to update BIOS/UEFI unless something is wrong with your computer or you need to install hardware that requires a newer BIOS (typically CPUs)
That said, because your PC is newly built, and that motherboard has been sitting for a long time and it's BIOS is badly out of date, it would be good to upgrade to the latest version, then leave BIOS updates alone unless a problem shows up.
I leave BIOS and Norton updates unchecked in GCC. But you can do what you think is best. If it ain't broke, don't fix it.
If it is neccesary to install BIOS/UEFI updates in order, GCC offers and installs them in order. Since F21 is offered for your motherboard, you can go straight to the latest version.