I managed to use cheat engine memory hacking to increase resolution to 4k and it works with variable 30-60 fps (tho mostly around 30fps) on RTX 2080Ti, still perfectly playable, and to me preferable due to having 4k screen.
If anyone wants to try and can't figure it out let me know and I'll explain details, but it's the most basic possible cheat engine usage and in this case it's surprisingly easy. Really wish author enabled all resolutions as is standard practice, and not a select handful, when the game can already run on any custom resolution.
Other than that, love the game and the technology! I'd put my hand in fire to see DLSS implemented in Marble Marcher as it's likely the single best existing use case for DLSS tech.