I see that you're on Windows. Open the Lightroom Keywords.txt file in a text editor and observe the number of lines. If you have more than about 1500 keywords (or 3000 keywords on some systems, depending on your display settings), as I suspect, LR will behave very erratically when displaying the Keyword List panel and the Keywords column of the Library Filter's Metadata browser. When you type the letter "a" slowly in the filter box, LR tries to display the search results in the Keyword List panel, and if the number of keywords in the result are more than the maximum 1500 / 3000, LR can lock up for up to minutes at a time.
With large keyword lists on Windows, people cope by keeping most of the hierarchy collapsed at any one time, so that the number of
lines displayed in the Keyword panel is less than 1500 / 3000. But this workaround won't help with the incremental search of the Keyword List filter box, since LR will display all matching keywords and their containing keywords
uncollapsed. The only workaround is to type the first few letters very quickly so that when LR gets to displaying the search results, they number less than 1500 / 3000.
The limit on the number of keywords in Windows LR and LR's bad behavior when you exceed that limit has been present since day 1. Adobe long-ago acknowledged the problem with a terse, incomplete help article:
https://helpx.adobe.com/lightroom-classic/kb/lightroom-doesnt-display-all-keywords.htm
It's pretty clear that Adobe has no intention of fixing this or even have LR behave more politely when the maximum is exceeded. The original bug report has had its internal tracking number removed and appears in the Discussion section of the Adobe forum, rather than the Bugs section (which is where bugs acknowledged by Adobe appear):
https://community.adobe.com/t5/ligh...el-prevents-scrolling-to-bottom/td-p/10854230
Similar symptoms afflict the Folders and Collections panels. The only complete workaround is to buy a Mac, unfortunately.