Downscaling/inverse supersampling/Resolutions?

Hi Everyone,

I have a computer-related question that i'm not entirely sure where to start looking for answers.

Put simply, I have an old laptop whose screen is no longer working. Was thinking about using it as a ML client. When I plug it into a 4k monitor that can support a resolution higher than 1336x768 the HD resolutions work fine. however when i plug it into a monitor with a lower resolution (e.g 1280x720), it gives me the Failed to find proper screen mode in GR2D error.

I can still play the game fine especially in its OG 800x600 resolution, but my question is, why can't my computer output a shrinked/scaled down version of a higher resolution on a small resolution display?. Is this even possible at all or is it a hardware a limitation of the monitor that is being used? Can this be changed or brute-forced albeit with a smushed, near-unplayable shrinked play screen area result?

Using CRU doesn't seem to work even after following the countless available guides out there, and I've found things like IntegerScaler but i haven't tried it with MapleLegends yet.

I guess my main question is about monitors, and how computers compute resolutions.

Thanks for reading.