I am not able to link my new created page to the navbar or anywhere else, since it’s not listed on [Link Settings > page]. I tried to understand the issue, but for me it seems as it would be a bug to be honest.
You’re trying to link to a specific CMS item page?
Yes you can do that, but to do it you need to get the slug of the collection and the item, and then link to it as a URL, e.g. /post/5-principles-of-effective-web-design
URL is the first option under links, the one that looks like a link.