VGA doesn't have a max resolution.
Higher the resolution, the lower the image quality will be (colors, clarity, and sharpness).
However, the DisplayPort to VGA converter circuit/processor in the adapter can be limited. A factor for this, is probably because it was designed for aged old projectors or CRT monitors, and ultra budget monitors.
VGA is a standard that is dead, and soon to be officially no longer supported by any graphics card manufacture.
I would strongly suggest to get a monitor with DisplayPort or DVI for the best image quality.
Use HDMI if you have no choice.