Well, those methods do work just fine in a conventional sense. However, what I'd like is a way that does not require any manual input, so that the monitor turns off all by itself every single time I haven't been staring at it, as well as in case I happen to forget to turn it off and also in case I am too lazy, since I am an average person, after all.
Besides, that particular PC is a home desktop server, and I need it running 24/7, since it has many connected devices, and booting/resuming is really a pain. Also, I mentioned that there are loads of running apps and opened windows--with tonnes of even more tabs in various browsers, therefore checking them all one by one every time I feel like it is not very practical and is time-consuming. I do appreciate all the suggestions, though.