How to minimize Thunderbird to the #Linux system tray
Birdtray is an application that allows users to keep the email program running in the system tray so that it is always accessible, and out of the way
It can also provide on-screen alerts for new messages
via the Flatpak app store, and via source code (though we do not recommend compiling it unless you understand programming or are an advanced Linux user)
https://www.addictivetips.com/ubuntu-linux-tips/minimize-thunderbird-to-the-linux-system-tray/