Always native resolution on Samsung Odyssey G9 57"

BeamNG – Current Version 0.35 and All Previous Versions:
When changing the game resolution via the in-game menu, only the user interface (UI) resolution is affected. The actual 3D game resolution always remains at the monitor’s native resolution — in the case of the Samsung Odyssey Neo G9 57", that's consistently 7680 x 2160 pixels. Neither fullscreen nor windowed mode, DirectX or Vulkan, advanced settings in Steam, changes to config.json, nor any other trick made a difference — everything was tried.

At a resolution of 7680 x 2160 pixels, the game unfortunately runs very sluggishly.
So, what kind of bug is this — and how can it be fixed?

I understand that not many users have a 57" monitor, and some might even grin smugly at this. But a bug is still a bug — and perhaps it could happen on smaller monitors as well.