barlow-700.ttf is Barlow Bold, the site's display face, from Google Fonts and licensed under the SIL Open Font License 1.1 (redistribution permitted).
It is here because the social card function rasterises SVG with resvg, and resvg has no fonts of its own. A Netlify Lambda has effectively no system fonts either, so without this the card renders its crests and silently drops every piece of text - which is what happens if the file goes missing.
included_files in netlify.toml is what gets it deployed alongside the bundled function; esbuild does not follow a runtime readFileSync path.