: You cannot hide the banner by adding CSS like display: none directly to your Apps Script HTML file. Google hosts the banner in a parent frame with a different origin, and browser security policies ( Same-Origin Policy ) prevent your script from interacting with or hiding elements in that parent frame.

If you are building the application exclusively for your personal use or a tiny tech-savvy team, you can block the DOM element locally using content filters.

When a user creates a script using Google Apps Script (for example, a Gmail cleanup tool, a custom Sheet function, or a chat bot), Google treats that script as an application. If you authorized it to access your data, it is now linked to your account.