Board Thread:Support Requests - Designing Your Wiki/@comment-45171933-20200522222638/@comment-9605025-20200524214010

Another difference between the Project namespace and the main namespace is that the Project namespace is not considered a content namespace. Therefore, it does not show in things like the article count in the local navigation. If you have 10 main namespace pages and 10 project pages, the local navigation will show an article count of 10 pages, not 20 pages. - Edit:

The two namespaces are no different with regards to protection. Both namespaces allow protection.