As mentioned the 1st Post, purpose of Pre-OpenCore GOP support is to enable the native Apple boot picker and early macOS boot progress bar display on non-natively supported GPUs, before, or even without, the rest of OpenCore.
So for example if you hold the Alt/Option on the keyboard straight after the Apple Chime, you will see the Apple Start-up Manager screen to select the the drive to boot...this is before OpenCore starts. If you do not use OpenCore, you will see Apple's native startup UI and progress bar on many of the listed GPU's on the 1st post.
That is achieved by adding to your existing Mac BootROM with the EnableGOP.ffs or EnableGopDirect.ffs.
For your RX580 EnableGop.ffs is sufficient.
The EnableGopDirect.ffs is for adding this feature to your existing Mac BootROM if have a GPU that requires DirectGopRendering setting in OpenCore config.plist file; e.g. Radeon VII GPU.
The EnableGop.efi and EnableGopDirect.efi are for adding this feature to your GPU's firmware instead of your Mac's firmware. There's a separate process for flashing your GPU.
Only one is necessary....flashing your Mac or flashing your GPU.
This is a really great feature addition to your Mac but you strictly do not need it if you are happy with the fact that OpenCore already shows you the boot progress bar and can even display OpenCore's Startup Managers (or boot picker) always at boot up or only if you hold the Alt/Option/Esc key (depending on how it's boot bicker is configured).
Read the warning of the 1st post !
If you do not know what you are doing then you could brick your Mac or your GPU !
