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You could always link other pages to this new folder and its content, no matter it appears in the side nav or not.
Note: Please use folders to organize and categorize your website. If you have only one single file to create, it is not necessary to create a folder for that. The folder name will appear in the URL and makes it longer to type. Please try to put related files and information in the same folder. This will help later to find the information faster.