Currently I have two monitors plugged into the two DVI connectors on an nVIDIA GeForce GTX660 GPU. When I maximise a windows of a programme, it stretches across both monitors. I would like to have a maximised window just on one monitor. How do I do that? TIA.
Have you checked under : Settings -> Devices -> Screen Display and check the setup that you have.
Also try the solution here in case it helps with your display issues, it certainly helped with mine: Enable fractional scaling for Ubuntu 18.04