filters – How can I display tags as categories?

I’m using the “Pages with category and tag” plugin because my website uses individual long pages as posts. I would like to make a gallery of the past posts (sort of like an archive section), but my theme can filter posts only by categories. I would prefer not to use categories but rather tags, since they are better suited for our content. How can I merge the categories and tags so that my theme can filter these pages using both?