I actually got this resolved. I ended up just using a base config.plist file instead of
@h9826790's (not that it was the .plist file that was the issue! Thanks btw) and making any edits I wanted to use on OpenCore. Everything worked perfectly! But then I wanted to enable NightShift and followed the directions on the first page. I had the same exact problem as before. My Mojave SSD would boot but not the NVME. I mounted the EFI and deleted the NightShiftEnabler.kext. I remembered that I had installed Lilu, WhateverGreen, and AppleALC on my NVME previously. OpenCore was injecting those kexts and Catalina was also loading them as well. I made sure to delete those kexts from my Cataline NVME, grab the latest, and stick them into EFI partition. Boom. Everything worked!
Double check and see if you have the same problem.
Speaking of kexts, what's the best way to get HDMI/DP Audio? Do I inject the kext using OpenCore using AppleALC?
EDIT: OpenCore is on my SSD not on my NVME. I don't believe installing OpenCore on an NVME is recommended.