Learned at Apple Genius Bar that the Sequoia 15.0.1 update has eliminated a chance to get back to the original classic email layout

Yesterday I inadvertently changed the look and feel of my email and attempts to recreate it as I remembered it didn't work. After trying to chat with an AppleCare tech, I went into the Valley Fair Genius Bar and the tech helping me quickly determined that Apple has eliminated a former function that allowed people to revert back to the Classic Email Layout. That layout worked well for me and I haven't been able to remember exactly what was different than what I have now but what I have now is frustrating and doesn't work. Any thoughts on this and a picture of what it used to look like would be helpful so that I might be able to get back there in another way would be appreciated. Sent a Linkedin Message to a product manager with responsibility for the Mail App but haven't heard anything. Thanks, Connie