Apple never implemented booting from APFS RAID arrays because they wouldn't want to add even more complexity to sealed containers.You are right. I have tried all the suggestions above and none have worked. It looks like I have to reinstall Mojave on the NVMe. Thanks for the reply again.
About the RAID, I searched through the 337 pages of this thread and didn't find much other than people not be able to see their RAIDs after installing Catalina and Big Sur. I had used the now obsolete thread (https://forums.macrumors.com/thread...to-make-catalina-work-with-macpro5-1.2183978/) and (https://forums.macrumors.com/threads/catalina-on-raid-with-apfs-on-macpro-5-1.2216730/) where I was able to run 10.15.4 on my Amfeltec RAID but updating to 10.15.5 broke it.
There reason I tried using OC and RAID was that some people earlier in the thread mentioned that the way OC works may pave the way for running macOS off of RAIDs too. I guess I can start a new thread and find out. My intention was to use OC on the RAID if it works if not Update my NVMe Mojave to 11.2.3 using OC.
As for mentioning a potential macOS install problem here was to literally find out if it was an OC problem or not. It may look so at first but it is not, but if other users also run to the same problem as me when using OC then these posts are useful for them to point them to the right direction.
OpenCore won't magically make booting from APFS RAID supported, it's an APFS limitation plus the way Apple now seal the container.