@LukeAlmighty so you gave two PCs plugged into one monitor. There should be a setting on your monitor to disable automatic input switching. I don't think that's a windows problem, if I understand correctly. It's just that windows will send a signal to a monitor that is sleeping or turned to a different input that it's time to wake up or switch. Consoles do this too. I think on ps4/ps5 you can turn that functionality off, but you can also do it on most monitors/TVs.