You can no longer go back to the old Gmail UI as the Google remove this feature. The change is taking place gradually and will be completed by the end of November.
Google introduced in February 2022 a new look and feel in a new UI. In June the change was visible to all, corporate and personal accounts. Until now you could use it or just enable the old UI.
The new design has no major differences as it only has a new side line, bigger buttons, and other minor visual tweaks. Now from November 8th onwards you can't opt out and stay on the old design, and everyone will gradually switch to the new one.
Google confirmed that the new Gmail design will "become the standard Gmail experience", with no option to revert to the old design (also called "home view"). The new design started on November 8 and will be completed by the end of November 2022 or the beginning of December. In our own personal accounts we can still go back to the old design, but we expect that to be gone soon.
Anyway, all this is informative space there were a few complaints, especially by people who they didn't like the always visible Chat and Spaces buttons on the sidebar, since practically nobody uses those two products.
