Dual monitor HDMI and VGA, different GPU's

I have a NVIDIA GPU GeForce GTX 950 (GM206-A) on PCIe and my main monitor is pluged on its HDMI port.
I also have the VGA output from my MB and need to use it on secondary monitor.

On W10, this setup works fine, but on Slackware Linux i can say that the monitor can receive input (it did not fall on energy saving mode) but is all blank. I have no clue on how make it work on Slakcware Linux.

The motherboard VGA port is probably on an integrated graphics chip. You can either try to create an X screen on it and use Xinerama, or bind it as a PRIME output sink.

But before getting into those advanced topics, a dumb question: can you just plug the VGA monitor into the GTX 950 with a DVI-I-to-VGA adapter dongle instead?

I’ve tried with Xinerama without sucess yet. I need help with xorg.conf , or another solution.

I know it’s may be possible an adaptor on DVI or Display Port, but i dont have one. The objetive is to make it work, as works on W10.