Thunderbird 91 Is Flying Soon As First Major Mail Client Update In A Year
Thunderbird 91 is finally set to offer import/export support for Thunderbird profiles, various user-interface improvements, improved GMail account integration, improved calendar settings, and tons of bug fixes and smaller improvements. The user-interface work includes enhancing the message reading UI, the message compose window has also been revamped, calendar UI improvements, and more.
More of the changes coming with Thunderbird 91 can be found via the beta release notes. While the betas have been out, the release candidate is imminent and Thunderbird 91.0 final is "coming soon".
There is also the Thunderbird roadmap for v91 and beyond that does outline more UI work, performance improvement hopes, and much more.