You are looking at the wrong folder. The leftmost panel in your screenshot is the root folder of your drive (evident from the names of the other three folders there). Your friend’s screenshot starts from their home folder (again, evident from the other folders there). However, as noted in other posts, your personal Library folder is hidden by default. You must either use Finder’s Go menu to get there or change Finder settings to reveal it. Or, you can open SketchUp->settings->files and click the folder icon at the right hand end of the row for Materials:
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