There isn’t a native method of bulk-exporting your Notes to a file. However, you can easily export individual Notes to a PDF file - repeating the process for each Note.
Using the Share button at the top of the Notes window (i.e., the square with an upward-pointing arrow), you can access the Share Sheet. From the Share menu, select Print to open the Print Options dialogue page - at the left of which you will see thumbnail images of each page of your Notes file. Before proceeding, refine the page-layout and scaling.
Next, use a two-finger zoom gesture (the reverse of a two-finger pinch) on any of the thumbnail images; this will open a print preview page. At the top of this page is another Share button; tap the Share button to open the Share menu (at the top you’ll, see that it says “PDF Document”).
From the Share menu, select Save To Files - choosing the path/location of your choice. Once you have saved your PDF file, you can close the dialogue windows as necessary.
This method of creating PDF documents works for every App that has a Share button. The description of the procedure is considerably more complex than the action itself.