This is not guide.... just my repo of the EFI for Opencore... but feel free to use it, if it suits you.....
Specs:
GA-z370-HD3
I5-8400 Coffee Lake
iGPU
NVME samsung 970 500gb
WD SSD 250gb
Water cooling
NO CFG unlock in BIOS
OpenCore 0.6.4
Big Sur 11.1
Everything works
One minor ACPI error (I dont even bother to fix it)
Fill in PlatformInfo in config.plist