1. If you are asking if Thunderbird V52 was real, yes there was one, back in 2017. It is no longer supported. 52.9.1 was the last of the 52 version point releases https://www.thunderbird.net/en-US/thunderbird/52.9.1/releasenotes/

2. NO idea where that version comes from you mention, but I am not aware of any official version of Thunderbird designed or built to run in ARM architecture, so I must assume it is one of the community builds. This old Wiki page indicates it is a tier two application, whatever that is. https://wiki.mozilla.org/Thunderbird:AArch64 and that there is a facility to build a developer copy. OR should I say bleeding edge build that comes with no guarantees as to actually running.

Google points to https://archlinuxarm.org/packages/aarch64/thunderbird for ARM builds of Thunderbird for ARCH Linux. That would be consistent with the details you posted. Their about page would indicate that they make the necessary modification to the source code to allow their ported applications to build. https://archlinuxarm.org/about

Thanks Matt.

Looking at the directory structure I see flatpak /var/lib/flatpak/app/org.mozilla.Thunderbird/aarch64/stable/7030558578c3938b000affe18e0ec6081bacde4e967dc818c4725ddb8d1786ee/files/lib/thunderbird-52.9.1 So I guess that tells me where it came from.

sudo flatpak uninstall thunderbird Found installed ref ‘app/org.mozilla.Thunderbird/aarch64/stable’ (system). Is this correct? [Y/n]: y

       ID                                       Branch         Op
1. [-] org.mozilla.Thunderbird                  stable         r
2. [-] org.freedesktop.Platform.ffmpeg          1.6            r
3. [-] org.gnome.Platform.Locale                3.28           r
4. [-] org.gnome.Platform                       3.28           r

Uninstall complete.

I'll try apt-get this time.

Thanks.