I want to use categories and tags also with pages (I am not interested in using posts since the page is for a university course). I can successfully add files to the _posts directory but when I add a file to the _page directory with the same Front Matter used in a post the page is not searchable and doesn’t appear in the category page.
I tried adding include: ['_pages'] to my config file but without any result.
My solution on this question was to use Collections - for example _cars as a folder and _dogs as a folder and you can iterate over items in each (check Collections in the Jekyll docs)
That approach is more elegant in a way than post categories as you have to update every post in a category in order to rename a category. But if you use a folder and configure you collection in config YAML file then it is easier to rename.
Tags are not so easy because a page can have tags so collections don’t make sense. That won’t affect you but it will give context for the links above since solving tags and categories is very different