I wanted to reply that I was having a very similar issue as the OP. Though it isn't a constant slow-down. Just an occasional one. But it does truly make everything feel unresponsive and like I'm using an old netbook or something. I was playing a game in which I usually get 60+fps, but during this slowdown, it goes down to 1-5 fps. Even when the game is closed, everything is just slow an unresponsive. Also the "System" process in the Task Manager list also shoots up to be a significantly high usage. Even then, I was only using 60% of my processor during this slowdown period, so it's not like it was struggling at 100% usage or something like that.
But this problem is intermittent for me. The most recent one lasted about 10 or so minutes? Though, other times have lasted longer. It's what prompted me to seek out some answers. Coming here, I wanted to help explain my experience. I've had this slowdown happen a few times now over the course of the last week or so that I've had the update installed.
After reading this article here: https://arstechnica.com/gadgets/2022/09/geforce-gpus-are-slowing-down-after-installing-the-windows-11-2022-update/
I'm going to see if updating my GPU drivers and the GeForce Experience software does help the situation.
So if you're using a Nvidia GPU, the above link might offer a helpful solution. I'd be more curious who is not using an Nvidia card that is also having this slowdown issue.
EDIT (10/14/2022): So far, I updated my GeForce drivers and other related software and haven't had the problem come up again. I'll keep an eye on it to see if it remains that way moving forward.