As the title says.
Will the graphics card still be usable and if so to what extent?
Thanks in advance!
You'll still be able to run whatever the last driver version was before support was discontinued with Windows 10, BUT Windows 11 is coming soon, and there won't likely be a new driver for any card that had support discontinued before it is released. So as long as you stay on Windows 10, you'll be good, but if you upgrade to Windows 11, you'll most likely have to change to a newer graphics card.
Strangely, you might have been better off getting a 750Ti, than a 760. The 750Ti is a Maxwell based card, and as such, it belongs more with the GeForce 900 family than with the GeForce 700 family. It will most likely remain in driver support at least until the GeForce 900 series is dropped, which most likely doesn't have more than a year or two left based on it's age. If you're going to upgrade, I'd wait until prices come down and get something like a 1050 Ti or one of the 1060 variants because they will be on driver support longer than anything from GeForce 900 family. If you buy a GeForce 900 card now, you'll be having to upgrade it again in a year or two if you still want to receive regular driver updates.