Locate the "Load Basic HTML (for slow connections)" link at the bottom of the Gmail "Loading" page. Click the link to switch to Basic HTML view form Standard HTML view.

Google updated a Gmail support article to say that the basic HTML view for Gmail will be discontinued in January 2024.

This time the scythe is coming for one of the company’s oldest features—Gmail’s basic HTML view. In January 2024, that simple interface heads for the great beyond.