If you use this URL to open Gmail’s basic HTML interface, you’ll probably see this message:
“Do you really want to use HTML Gmail? You’re about to use a version of Gmail designed for slower connections and legacy browsers. To get all of Gmail’s features, including inbox categories, images, and quick actions, please use the latest version of Gmail (recommended).”
You can click “Take me to latest Gmail” or “I’d like to use HTML Gmail” if you really, really want to use it.