Not a doctor and you may want a doctor’s opinion on this stuff…
But I’ll mention what you’re describing is very much brain fog like symptoms. It’s more well known as a long covid symptom nowadays however it did always appear as a symptom of other infections. I have an older family member that went through an intense encephalitis infection (for him it started out with a viral mosquito infection, west nile virus to be specific) and since encephalitis affects the brain he eventually recovered with brain fog symptoms among other things.
Thing is that healthier/younger people can be infected with viruses leading to encephalitis and be asymptomatic (no symptoms) during that time, but down the road long term symptoms can show up like brain fog. Yes, like long covid, but other infections can lead to the same result is what I’m getting at. Getting some blood work done with a doctor would narrow down or rule out stuff like this.
Linux would make more sense but if you’re dead-set on Windows then I guess you could try Win 11 Pro (or Enterprise) with whichever debloat tool you prefer. I’ve had good experience with Win11Debloat (https://github.com/Raphire/Win11Debloat).
Don’t expect too much with 8GB RAM but at least you can start out removing the AI stuff, Windows Store apps, etc. to trim down the bloat. Be prepared to have to re-run debloat scripts and/or re-install Windows, Microsoft likes to add new types of bloat post-install.
And keep an eye on any and all apps and services that are configuring themselves to auto-start on Windows boot, you don’t need any optional stuff to auto-start and take up memory in the background if you’re constrained to 8GB RAM.