usb does not as such carry video signals it's a general purpose serial data interface it require special dongles which act as external usb graphics cards
https://www.displaylink.com/products/usb-adapters
more
https://www.google.com/search?q=mac+usb+video+card&oq=mac+usb+video+card&aqs=chrome..69i57.2933j0j7&sourceid=chrome&ie=UTF-8
but it should not be such a big problem the back of my imac 2011 looks more or less like yours the 2 ports in your photo most to the right are thunderbolt ports
I use the thunderbolt to dvi as seen here
About the Apple Mini DisplayPort adapters - Apple Support
you should be able to use the thunderbolt to vga also displayed in the link
I've been using my adaptor with a variation of different monitors (samsung, dell and now asus) since 2011 without problems
these days the asus monitor which has several inputs are shared between second monitor for the imac, xbox screen and monitor for a windows desktop