MacOS Sierra switches to default graphic driver when connecting VGA monitor

[prototypeDCB]

Hello to everyone,

I have updated from OS X El Capitan to Sierra 10.12.1 and my secondary display has stopped working. My main display is a Dell U2414H, which is connected through DisplayPort and works fine. However, the problem arises when:
- I connect both monitors (the secondary display being an LG E2211). When I boot I only get an image on the secondary VGA monitor and the graphics driver switches from Nvidia Web Driver to the default OS X driver. Selecting Nvidia drivers and rebooting doesn't work, as the drivers are reset again to default.
- I connect the main display only and Nvidia drivers work again, but if I connect the secondary display the OS doesn't detect it. If I reboot then I'm back at problem #1 again.

The thing is both displays worked perfectly when I was on El Capitan. Since the GTX 970 doesn't have a VGA port I use a passive VGA to DVI adapter. To reinstall Nvidia drivers i referred to this post:
https://www.tonymacx86.com/threads/solving-nvidia-driver-install-loading-problems.161256/
Specifically problem 6.

SPECS:
I5 4690K
GIGABYTE Z97 GAMING 3
MSI GTX 970
(I don't know if that matters too much but I also have 16 GB of RAM and OS X is installed on and SSD, dual booting with Windows 10 and using Clover)

Thanks for answering!

 

[slim.jim]

VGA is likely the issue, it is hit or miss with OS X and has been for sometime. You could try an active adapter which will appear as being connected through DVI to the OS.

 

[nobodynose]

Apple hasn't released hardware with a VGA port in many years - VGA is unsupported in macOS (even though it did work in some isolated cases).