Fresh Windows Install?

I’m not sure if this is the right place to ask this, so if it’s not please just let me know. We had a gaming pc built for my teenage son a couple years ago. I researched a ton and handpicked all of the parts, and we were lucky enough to have a family friend willing to do the build for us. It’s been running great until a couple months ago when his games started lagging significantly. Of course, as a teenager he didn’t say anything to me and instead decided to delete all of his games and reinstall. The problem got worse. I’m thinking he likely did not uninstall the games/apps correctly. He’s also seriously low on SSG.

I’ve double checked that all of his drivers are updated and went through and uninstalled games/apps he’s not using, but it doesn’t seem to clear up any significant space. I’m to the point that I’m thinking a fresh install of Windows would be the best option, but I’m hesitant to do so. Can anyone tell me if I’d have to reinstall all of the software for GPU/CPU/Motherboard/etc if I do this? Thanks!