[jkrejcha]

At least on Windows 10, which I still run, pretty much all of the "explorer is slow" issues are caused by shell extensions.

The problem is a lot of the times they make poor assumptions (like "if a process is running it'll respond instantly") and honestly the tools that exist for determining what is at fault are... well effectively nonexistent[1]. This goes even for 1st party shell extensions. Part of the problem is these almost inherently violate what I consider one of the golden rules of GUI programming (don't block the UI thread) and there's a lot of historical reason for this, but it is often the cause of stuff like "explorer.exe uses 100% CPU" or "right-click takes 30 seconds"

[1]: There's a SuperUser post in which the recommendation is effectively: manually binary search for culprit shell extensions yourself (https://superuser.com/a/577935/312312).