First, i'm also a vanilla to all this, but there are some more questions to ask. Bios Version and cpu as an example.
my start was like yours, and now it is the same. For me it looks like, that there are different Versions with complete different behavior. I tried a lot and only one efi work for me. you can find it a little bit back. Now there is no way, to bring it to catalina 10.15.5 >Beta3
. not with the efi from Shumbola and not with the OC Version from Amateur85.
Like i say, i'm a vanilla, but it looks for me that there are different S200 with different behavior in usb and ssd(NVME).
If i start with the Vorke V8 Howto, it looks like that somewhere in the installation the usb-connection was lost. later i had massive problems with NVME and it was not only one brand. i tryed a 970 from samsung a ssd from wd a asgard ssd and always without progress. than i find the efi form tnjens (Efi 2.zip 26.04.) and the installation was easy. But like i say, if you want to test it, you need a older Version of catalina because with 10.15.5 you become a black screen with hdmi and/or DP if you use the UHD630.
i tryed a lot the last days, but without luck. The efi from Shumbola was not bad for me, but it stops in the middle of nvme activation if i understand the srcreen output right. i only had one time luck with some settings for the UHD but this will disable the UHD to VGA mode. Any other try ends in a running system with black screens.
So i'm back to 10.15.3 because that's the only installation files that i have before 10.15.5.