Look I’m not tech savvy at all, but I have been using windows for a very long time. Take the following with a grain of salt. Here’s my two pennies:

1: Windows has a tendency to run background processes as soon as it detects you are idle, and once those processes start they don’t stop cleanly if you resume activity. I find they will stop for good only if I do something that forces clearing RAM to start a RAM intensive process, such as restarting a game in your case.

2: The best deterrent to windows doing this shit in the background is to purge as much bloat as you can, and turn your wifi off if you are not using it. Turn auto updates off (or delay as much as possible). My laptop behaves pretty well on idle if it’s offline.