I have an old 2013 Notebook with Intel integrated graphics and a discrete GT525M GPU. Being not at home for christmas today, I started a game on it for the first time in years. It did not launch, DX 11 title. Another crashed but worked in DX9 using the integrated graphics. Google is your friend and revealed to me that the function is broken in all Windows 10 drivers and was last working in version 350.12. I installed those, and sure enough all the games refusing to work before run fine again. Also seems like Nvidia were made aware of that long ago. Why did that not get fixed ?
As long as some drivers are semi-functional at least some of the time, Nvidia doesn't give a f*** about the ongoing issues with Optimus and continually deny that any such problems even exist. Check the thread here: https://forums.geforce.com/default/topic/860554/geforce-mobile-gpus/windows-10-and-optimus/1/ Well documented problem that is reproducible by virtually anyone with an Optimus GTX 9xx/10x0 card, and also apparently impossible to be fixed. Nvidia points their finger at MS, and then MS says the problem doesn't exist, and any problems are Nvidias fault. Not sure where Intel HD lies in all of this, but it probably has a role to play in the BS as well.
Well, older Windows 8.1 drivers working is a strong pointer towards Nvidia for sure. But I'm giving them the benefit of the doubt regarding the newer WDDM version in the Windows 10 drivers and the DX12 functionality. I simply don't know enough to pinpoint anyone's fault.
In an Optimus setup, the Intel chip is the master, and the NVIDIA addition is the slave. So I would start looking at the Intel drivers first.
Chastity is correct. Nvidia is not responsible for Optimus issues. If anything, they should be praised for providing decent driver support for Optimus over the years, including for Windows 7 (still). Reminder that Intel drivers for the latest models do not even support Windows 7. Thankfully, these kinds of gpu laptop setups are going the way of the dodo as gpu power efficiency has been steadily improving over the past few years. That means that even budget laptops will be running a dedicated gpu soon.