Dear Greg --
I have the same problem. I haven't tried any of your approaches yet,; I'll need to set aside a whole day. But I just want to give you a big thank you for composing the email, and assembling instructions that are as clear as could be given the little information you have.
Each update in 2020-2021 has noticeably slowed my computer, to the point that it's now taking 45 and 50 seconds to load routine pages (like Firefox startup screen, gmail screen that lists 50 messages, etc.) The updates of 2021 are especially bad.
Microsoft, please stop. It seems that there's a finite set of good ideas for operating systems. It seems that that finite supply was exhausted in 2004 or so. That was the year that the ratio of worthless/bad/slowdown-with-no-benefit/bury-useful-things-under-uselessly-deep-menus changes to Windows crossed over the ratio of good ideas (Vista and Office 2007). Please stop. Please stop. Please stop. Or else give us a switch we can set to disable all updates except urgent security updates.
Thank you Greg, no thank you Microsoft.
David