SOLVED via using a Emulated NVRAM distribution of Clover with a couple of kexts. If you want, I'd provide my EFI folder.
This was my problem, and I hope it'll be your solution also!
Edit: Only in Mojave. I've not tested Catalina yet, since it's not secure (even in real Macs!)
I've did succesfully my first Hackintosh and it didn't be very problematic (I'll be posting it in a few days).
But now I'm trying to build a hackintosh for a friend and I'm encountering the same problem again and again. I've tried to change the motherboard, but nothing happens...