Mostly new control panels like Recovery, Trouble shooting, Windows Mobility Center, Storage Spaces, etc.
Also, am having to apply the icon set multiple times for it to apply all the changes.
Microsoft is changing almost all of the icons for Windows in the upcoming 21H2 (Sun Valley) version, and I'm sure there are going to be a lot of folks looking for ways to either change them back or to something completely different. Even if you have to raise the price, it would be worth the expense.