Kepler's are older and Mojave compatible, GT/X 600's/700's-but there are few threads already explaining a Mojave upgrade and the cards that are compatible. If you have a dedicated graphics card on your logic board, stick with that vendor to avoid conflicting drivers. Welcome to the community, read what's already been discussed-I hope we all can help each other. Thanks!
Final note-exploring a logic board upgrade may be an alternative solution as well as allowing native Mojave support, but do your research to ensure it possible-2011/2012 had a few things slip through with the 15" MBP's rush to Retina Display. I'm not sure if they've made such similarities in logic board design, or in other models during that year change. The non-Retina 2011 and non-retina 2012 boards were physically identical in shape/mounting/cooling, with only a minor modification to the VGA cable to the 1400x900 display.