"ERR_GFX_D3D_DEFERRED_MEM Out of memory. Please reboot, close other applications, and ensure your computer meets the minimum requirements."
^ Unfortunately I had the opposite experience.
Previously I got that error consistently during loading screen after I installed less than 10 mods, including a few .asi mods. (all of them were downloaded from this site) After that I discovered this gameconfig: "A Modest Memory Pool Booster for LML - Performance GameConfig XML," although it doesn't actually add any memories to the game, but I was able to load the game and play for hours.
But still, with that gameconfig, this error can popup unpredictably during regular playthrough, although it happens less often now; which was odd because the game wasn't trying to spawn anything "crazy," I did not have any applications like Google Chrome, or even Discord open in the background, and my PC exceeded the minimum requirements. Also since the majority of the map are just landscapes which shouldn't take too much game memory to load.
The only explanation/theory I can come up with is, there is a in-game "memory cap" for RDR2, just like GTA 5, and once you reach that "memory cap" somehow with mods, without any other mods to increase the default memory limit, the "out of memory" error will appear regardless of your PC sepcs.