I can't help because I don't run Windows, but maybe you can restore a previous working version?

I had history all the way back to Oct. 16th (believe that's when I upgraded). I did follow the steps in your screen capture and it worked (since Clear option didn't show up). It worked. Still what a pain. I did find out that if I uncheck Send my activity history to Microsoft, temporarily change to another setting (I chose Microphone) then go back, the clear option becomes available. Weird bug. Still, the Clear works once you see it doing this so don't have to use the steps you provided again. Hopefully Microsoft will fix this behavior. Again, you need to uncheck Send my activity history to Microsoft, temporarily go to another setting, then go back. Then you can go ahead and re-check send my activity to Microsoft and also clear activity history. Of course if you go to another activity and come back, you will no longer have the Clear option, but that's OK; can get Clear back by doing the steps that I spieled. lololl

Thanks for pointing this out; way too much things to look at; just want a month (actually it hasn't been a month yet; I bet after a month it will clear older entries; I'll wait to find out).

So the software maker assumes the users can't remember what their tasks were?
So the users are supposed to send their tasks to the software maker so they can be reminded what they were doing.

That's just insulting IMHO.
Sometimes I do forget what I was doing but because I'm just 1 person on a planet of 7.8 billion people, it's safe to assume it was insignificant.

Hi mackenzieh.
Here is how to switch off Timeline in Win 10 version 20H2.

No a clean reboot is different to a clean install.

A clean reboot starts with a minimum set of drivers.
https://support.microsoft.com/en-au/help/929135/how-to-perform-a-clean-boot-in-windows

Free advice from a retired IT guy.
If you are going to use an unreliable operating system then you need at least 2 computers.
Owning 1 computer and running the Seattle OS will give you stress.

I've been using Ubuntu for decades because it's well supported and stable. I did skimp on hardware by using second hand stuff but in the long run it's best to go with reputable brand hard disks, ram and motherboards and open source software.

Free advice from a retired IT guy.
If you are going to use an unreliable operating system then you need at least 2 computers.
Owning 1 computer and running the Seattle OS will give you stress.

I've been using Ubuntu for decades because it's well supported and stable. I did skimp on hardware by using second hand stuff but in the long run it's best to go with reputable brand hard disks, ram and motherboards and open source software.