Have you took a look on your system, while generating a map and/or starting a game? I'm still not sure where the problem is. OoM while generating a 8k map or while starting a game on a 8k map?
Memory usage while map generation is different from loading a game on a fully generated map. Generation might even need more memory at some points that just playing on it.
Take a look on your memory usage with a tool that shows or even better logs usage into a file while the game is running (maybe MSI Afterburner or HwInfo64 <- That especially also shows the virtual memory usage). Take a look at how much memory is especially used by 7d2d and how many is used by Windows and maybe by running programs in the background.
12GB memory is not that much. However it should be enough to run the game. I assume you already tried closing all unneeded programs? I hit 16GB easily with all my usually running background programs and 7d2d.
Also a 7200 Ryzen does not exist. The only ryzen i found with integrated Vega 10 is the 2700U. And there the Vega 10 uses the main ram too. So if you have 12GB in the system, even 1-2GB (or even more) might be additionally dedicated to your GPU.
I had twice the problem now that windows somehow @%$*#!ed up memory usage. It said virtual memory was used up to 99,9%, however there were stil 20GB of ram free and i had various oom crashes, not just with 7d2d. A reboot fixed that. And this is a windows problem on my machine, not related to 7d2d.