I have not personally done this, but you might be able to change the default fallback mode, and if lucky, then the VGA monitor would work with that mode:
https://forums.developer.nvidia.com/t/why-and-how-cboot-select-different-resolution-with-different-display-monitor/148067/4
What it comes down to is that the driver will only accept modes via EDID, and there are some restrictions on that as well (such as no interlaced modes and no extension modes). If a suitable EDID is not found, then it will use a fallback mode, and you can possibly edit the kernel to use a fallback mode which is convenient to you.