Posted in Steam Machine / GabeCube
It's just the video memory which allows the graphics card to store and quickly access graphical data like textures and frame buffers, which improves performance and visual quality. If you're running in native 4k, naturally the requirement for more VRAM goes up, as it does if you pile on more advanced visual features. Once the VRAM is full, many games will suffer performance problems, like stuttering or texture pop in etc. Modern upscaling technologies like FSR and DLSS allow you to have a "4K image" but without some of these penalties and framegen can insert fake frames to boost performance (at a cost in lag/responsiveness). Assuming the GabeCube is around a mobile 4060 in power, I think it'll be capable enough in most games at 1080p native, medium detail, and then using framegen/upscaling you might be able to push it further.
There aren't many modern titles that are backbreaking for a GPU, and those that are, are normally poorly optimised. Avowed is a good example, it probably wouldn't run that well on a GabeCube. I think people's main concern will be about the flood of upcoming UE5 games, that, to date, have followed Avowed in running pretty shockingly on midrange hardware.