My cheap-ish Samsung (cheap for a QHD) has an HDMI and a DisplayPort input. If I hook up a laptop to each input, both laptops think the screen is on- even the one who is not currently being displayed.
I have a Dell U2720Q monitor that accepts HDMI 2.0, DisplayPort 1.4 and USB-C. I use USB-C because the monitor acts as a hub for a range of peripherals (keyboard, mouse, webcam, speakers, etc.etc) and ...