If you're looking at a large page of text documents on your Windows PC, you might want to make your file icons ... you'll want big icons to see what each picture looks like. In either case ...

it may happen that File Explorer does not display the offline file icons correctly. You can identify an offline file by the overlay that shows an “x” character in the lower-left corner of the ...

This is what my selection looks like. To break it down simply, you need two things: A folder with all the icon files for your taskbar apps. The file has to be in ICO, EXE, DLL, or ICL format.