“Keep Black” is one I wish I knew about, but just recently found. It’s a simple app you launch to make your screen black.
If you have an OLED, this is really great as you no longer use up your panels lifespan and power consumption goes to almost zero with all pixels off. I use it whenever I’m playing music through my system and don’t need the display running.
Just to add to this. Instead of Steamlink, check out Moonlight. It looks offers reduced latency and significantly better visuals (better compression + higher bitrates). It’s free also.