One long running Windows bugbear is that SKP files etc show an image in their file-icon, but SketchUp’s .SKM [material] and .Style files do not [of course they do show up in SketchUp itself but use a generic icon in Windows Explorer].
There are paid 3rd party apps to fix this, but the free ones [e.g. SageThumbs] fail with SKMs, until now. There is a good free and safe alternative called ‘Icaros’. It’s simple to install and use. You need to add this to its supported filetype lists -
;.style;.skm
and restart to see your Style and SKM files images in the Windows Explorer file-icons…
https://github.com/Xanashi/Icaros/releases/tag/v3.3.5
