I have similar suspicions. I have a decent but not spectacular company Thinkpad. When I first got it, it was super-fast; it didn’t matter that sleep very quickly turned into an automatic shutdown, as it booted in mere seconds.

Gradually, over the past 9 or so months, it’s just become progressively worse and worse in a range of ways. It might be Windows updates, but the magnitude makes me suspect it’s layer upon layer of corporate management and security nonsense.

Could also be a temperature throttling problem caused by dust or a stuck fan. My old work Laptop suffered from that, and recovered after I cleaned it.