Comment by exikyut

> The old HTML mode is still there but is hard to get to and is supposedly going to be phased out.

Can you share any info on how to access it?

Trying https://mail.google.com/mail/u/0/h/ (the /h/ on the end being the old way to get Basic HTML mode) just redirects back to the normal view and changes the loading screen to say "We're loading the latest Gmail version."

Setting my user-agent to IE6, or IE11 in compatibility mode, produces a "Temporary Error (500)" screen that says "We’re sorry, but your account is temporarily unavailable. We apologize for the inconvenience and suggest trying again in a few minutes. You can view the Google Workspace Status Dashboard for the current status of the service."