I had to add the ACPI entry for the second nVME and mapped it to ANS2 to make it appear as an internal drive (otherwise, it appears as an external yellow drive).
The biggest source of frustration was that booting from my SATA drive was horribly unreliable. I had tried to create a minimal config.plist but was told to use sample.plist as a basis so that involved a lot of trial and error. After exhausting all options, Pavo on discord basically felt like something was wrong with the hard drive and...he was actually right. I changed to another SATA drive and this one boots reliably every time.