A repost of the following from me is on https://www.reddit.com/r/windows/comments/hd61wi/windows_search_slow_on_windows_10_v2004_how_to/
Both of the following things fixed my issues. I was expecting only one, but my god this was deeper and worse than I feared. Microsoft, y u break?
There are a few things in task manager you might see jump up in Disk usage after clicking on the search...
1. The COM Surrogate process ( https://www.tenforums.com/general-support/37841-disable-webcachev01-dat.html ). If in Task Manager you this process with 3EB3C877-1F16-487C-9050-104DBCD66683 in the Command Line under "More Details" (you get this header sort option by right clicking on Name, and checking the box for "Command Line") then this is the This is WebCache, the implementation Search uses to get cached web entries (Even if Bing Search is disabled as per https://www.windowscentral.com/how-fix-taskbar-search-not-working-windows-10)
Open Registry Editor (as Administrator) and then search for the key 3EB3C877-1F16-487C-9050-104DBCD66683 and right click, hit permissions, hit Advanced. Set Ownership to your user (not administrator) by hitting Change. Enter your computers username and hit "Check Names" and hit OK. Now hit "Enable Inheritance" and click OK.
Now you can delete the key, so right click and delete.
2. The Nahimic Service ( https://rog.asus.com/forum/showthread.php?110279-Purpose-of-Nahimic-with-Realtek-Audio-Driver). If in Task Manager you see taskhostw.exe with 222A245B-E637-4AE9-A93F-A59CA119A75E in the Command Line, you might have ASUS ROG stuff installed, like Sonic Studio (along with other things that may be related including possibly sound driver/etc.)
I opened "Task Scheduler" and I saw this was the problem by hittning "Scheduler Library" and sorting by Running. I then hit the search again to trigger the slow crawl. Task manager shot up disk usage with taskhostw.exe and I "Stopped" the task it belonged to. In my case, this was "Nahimic Task." I right clicked and hit stop and "Disable" on both of the two that were in that list.
Now there is also a Nahimic Service. I'm not sure if this was the problem, but to keep everything tidy I went into Services and disabled this too.