Well, I found out a few days ago that my "solution" for Red Dead Redemption 2 only prolongs the time before crashing from around 20-30 minutes to 2-3 hours, but I also fortunately seemed to have found a REAL solution/workaround after turning all the settings down to "Low" and then testing each individual graphics setting at its max one at a time and testing the game for several hours (or until crash). In doing this, I found that having the "Reflections Quality" set anywhere above "Medium" caused the entire system to crash with a Green Screen/Black Screen; turning down "Texture Quality" just prolongs time before crash. Also, it seemed when setting "Screen Space Ambient Occlusion" anywhere above "Medium", it results in the game randomly crashing back to the desktop with a message "Unknown Error: FFFFFFFF"...
After turning "Reflections Quality" and "Screen Space Ambient Occlusion" down to "Medium", I have played the game for several hours at a time and left it running in the meantime for 2 days straight with no crashes and/or reboots (with "Texture Quality" at "Ultra"; I now have FSR2.0 Disabled because of irritating tracer/ghosting effect)...