Hello and thank you! I've taken all of the steps c:
It's difficult to be specific about which folders, because I only remember to go through occasionally, but I find that things I've deleted before in my program files folder and AppData local and roaming folder reemerge. Although for AppData, that's typically what will happen when I'm using programs, but they include things for programs I don't have installed like spotify, skype, and others. When I delete these folders, suddenly my computer runs like a dream, but when I come back the next day, it's bad again.
Something I've done is turn off windows search, because it would show as eating all my CPU in task manager, and because nvidia would show searchapp.exe as running on my GPU. Nevertheless, it runs in the details tab of task manager. The same is true of textinputhost.exe and startmenuexperiencehost.exe, which appear to use my GPU at times, and my computer runs better when close them. Sometimes they stay closed, sometimes the return immediately. Settings in Nvidia control panel often change by themselves and performance improves when I fix them.
I suspect my issue is a rootkit, but honestly I have no idea what's going on with my computer.