Hi Awsmits,
Based on your post about it being a 2012 iMac, I am presuming that the USB ports are USB-A and not USB-C. I am also presuming that the external monitor using VGA/DVI is only 1080p and not 4K resolution.
Based on those assumptions, we have a list of products on our
website here that all meet those requirements. The drivers you will need are the standard DisplayLink drivers for MacOS that can be downloaded from our
website here.
Hope that's helpful.
Regards,
Andrew