You get the source code of the examples in the browser under Windows by pressing Ctrl with U (in Apple Safari probably cmd alt U ).
You can also type or copy view-source: in front of the link.
In the collection you can see what it’s about by the pictures and the short title.
I enter Sphere, for example, in the browser search on the 2021 discourse.threejs.hofk.de page and get the highlights and can navigate from example to example.
Firefox, Chrome is is similar
The best thing to do is to download the individual years and unzip the file on your computer. Then you have the html files in the folders and can open them with your favorite editor.
See link GetSources at the bottom of the page * discourse.threejs.hofk.de ,
and also the other references down there.
Good luck 