Why does Task Manager show 100% disk activity for a prolonged period?

My other laptop, the one I use for most of my work, is currently showing disk activity at 100% and has been like that for a solid hour or more now. I can't do much of anything with that laptop because it is so pre-occupied with writing to the disk. I get that the computer has to write to disk occasionally but this is ridiculous. I even tried rebooting the computer but it just went right back to 100% on the disk activity after the reboot.

I sorted the list of tasks to see which ones were doing the most writing but it wasn't always the same one or two. System and Firefox were certainly the ones at the top of the list but many others were there for at least some of the time.

Is there anything I can do about this? I've had this issue a few times before over the years and I've never figured out why it happens. It seems to sort itself out eventually but the computer is virtually unusable for hours while I wait for the disk activity to go back to normal levels. I have things I'm trying to do with the computer so this is very frustrating.

As I've been writing this, the disk activity has finally gone back to lower levels briefly - sometimes even to single digits - but has also spiked up to 100% again a few times.

I'm running Windows 10 Home 21H2.

"System and Firefox were certainly the ones at the top of the list but many others were there for at least some of the time."

System, can be associated with Search indexing, that can be configured to index fewer files. Search the settings.

Settings > Search > Searching Windows > ....

As it says, user activity should minimise Indexing, but if you have a ton of items it will tend to go on a bit.

Firefox, I don't use, but any Web Browser has multiple settings to be looked at.

Then you just continue to look at others topping the list, do some research, often it is something relatively simple like a couple of settings in an application.

Eventually you will get a leaner and meaner machine.