Broken link
Opening the issue here, despite that this may the not the ideal location.
You link at an archived repo:

https://clearlinux.org/developer
You also fail to specify, what happened with the project. Is there a replacement? One planned?
Welcome to Clear Linux* OS Docs. Thanks for submitting your first issue.
I also come across several broken link which I bookmarked as technically references before. While documentation links are broken now possibly due to their transition from clearlinux.org to GitHub pages (again?), the project is still actively updated and community forum has new posts every day.
Yes, as Vinfall notes, we're in a transition period right now, and a there's a lot of broken links. Once we get the clearlinux.org and documentation websites set up how we want, we'll start working through all the links and updating them as necessary.
There are webpages, who scrape through your whole page and list you all the broken links.
https://www.deadlinkchecker.com/
The fact that this training is no longer maintained has now been noted in that section.
There are no plans to update it, however the basic information there is still informative and generally still useful.