I use a mix of Evolution[0] (GNOME's Thunderbird) and Geary[1]. Geary has a very nice UI, and can become mobile-like, and Evolution has much more support for automations and other niceities.

There's also alps[2], if you want a web based solution. I love it as well, though Geary is my most used solution.

[0]: https://gitlab.gnome.org/GNOME/evolution/-/wikis/home

[1]: https://wiki.gnome.org/Apps/Geary

[2]: https://sr.ht/~migadu/alps/