So, I got a new Samsung Odyssey Neo G9, awesome display but it's also functioning as a heater and eating a lot of electricity. Therefore I want to keep it off when I'm not using my computer. That used to work fine, but a few weeks ago Windows no longer turned off my display and stopped going to sleep when I didn't use my computer. I was pulling my hair to figure out what was happening, I changed power settings, sleep settings, screensaver settings and so on but nothing helped.
Then I found I about a nice little command:
Run this in the terminal and you'll see what is keeping a lock on the system.
In my case, Adobe Creative Cloud caused the trouble:
PS C:\Windows\system32> powercfg -requests DISPLAY: [PROCESS] \Device\HarddiskVolume6\Program Files\Adobe\Adobe Creative Cloud\ACC\Creative Cloud.exe Video Wake Lock
Why on Earth would they keep a display lock for a background process like Creative Cloud? Anyway, killing that process and making sure it doesn't start with Windows fixed the problem for me. Next thing I'll file a bug report for Adobe to prevent this behavior.