Ola !
Just followed your tutorials and successfully installed Catalina 10.15.6 on minimal config (mobo Gigabyte Z390 Designare and NVME + Sata SSD, nothing else). Just got an issue with the black screen after boot, which I fixed by adding the -igfxvesa parameter.
I'm at the final step for DSDT patching, so.. here is the file :]
Thank you so much for your amazing work !
Send me admins-iMac.zip