The 3dprint beginner guide, “How to Enable STL Thumbnails in Windows 10?” (https[://]3dprintbeginner[.]com/how-to-enable-stl-thumbnails-in-windows-10/) relies on a GitHub repo that was last updated over a year ago.
There is always the chance that the project is no longer maintained and could be completely dropped. I would like to see an alternative offered since the latest version of Microsoft Power Toys enables thumbnails for STL (among other formats such as svg, etc.). You also get a host of other benefits as well from using this official Microsoft tool for windows that just plain work straight of the box. There is always the chance that Microsoft drops support for Power Toys as well, but with its long history I think it will probably outlast stl-thumb by unlimitedbacon on GitHub.
Official Links:
Install with Microsoft Store from the PowerToys page.
https[://]aka[.]ms/getPowertoys
Install with Windows executable file via GitHub
https[://]aka[.]ms/installpowertoys