What i mean is am i free to use other free services like github pages to host my projects?
As long as the work and code are viewable, you can use whatever you like.
Lots of us use gh-pages
If you can, use github pages.
Codepen is suggested so that new coders can jump right into projects without worrying too much about configuration.
Use anything you like. I do all of my FCC projects locally and host them on my own website. When I submit a finished project, I just put in my actual web URL instead of a link to codepen. No problems for me so far!
The project links are evaluated. We click the link review the project. I also suggest when not using codepen or other simple front end technologies (back end stuff) putting a github repo link in the project under about. Personally, I will be working on the Rogue-like dungeon crawler on an express server for hosting micro-API’s and hosting on Heroku. So it is personal preference.
From experience, when I check projects for green lighting for non-profit project source code is reviewed, I generally look for github links to verify that the code it all yours, or attributed.