Thunderbird is an independent, community-driven project that is managed and overseen by the Thunderbird Council, which is elected by the Thunderbird Community.
Fair nuff. Sometimes it's just overwhelming getting information of something I can't do anything by. Like oh great another thing that's going wrong rn... Woo hoo
You could switch to KMail, which is developed by the KDE community, organised in KDE e.V., an actual registered non-profit.
Or Evolution, developed by the GNOME project, organised in the GNOME foundation, another registered non-profit.