Somewhat of a solution! I wanted to post a discovery from a couple of months after my previous post. My setup is a dual boot with a separate Windows drive and I started to find that once I ran Windows and restarted to in order to boot into Catalina that the crash issues were definitely present. I discovered randomly that if I shut down the system completely, wait about 10 seconds and re-boot directly into Catalina from Opencore the problem with the 5700xt crash magically disappears. There's still the occasional flashing in the menu bar area but the system is completely stable and does not crash. Once Windows is loaded, no restart will boot a stable system. It's only after shutting down and waiting a bit that there's any stability. Could it possibly be related to NVRAM or something? Some sort of memory flush issue before booting into Catalina? Anyway, I was glad to have at least solved this for a time. On to Big Sur where new challenges and bugs will surely await!