Add your own Handlebars partial directlyto Eleventy

.eleventy.js

// via https://www.11ty.dev/docs/languages/handlebars/#optional-set-your-own-library-instance
module.exports = function(eleventyConfig) {
  let handlebars = require("handlebars");
  // see https://handlebarsjs.com/guide/partials.html#basic-partials
  handlebars.registerPartial("name", "Handlebars syntax");
  eleventyConfig.setLibrary("hbs", handlebars);
};