const editorInitConfig = {
  // ...
  menubar: "file edit view insert format table custom",
  menu: {
    // ...
    custom: {
      // icon: "emoji", this option does not exist
      title: "Custom",
      items: "...",
    },
  },
  // ...
};

I’ve tried some custom injection to no prevail, I attempted to inject an SVG after the editor initializes on the page.