I thank both of you. I am glad others see it the same way!
True, there are the mentioned solutions, snap package and PPA. Unfortunately they only help us. We know how to include a PPA, how to install a snap package and migrate data, that there is an action needed at all.
But the masses remain threatened and most don’t even know it. They just use the preinstalled Thunderbird and don’t read IT news about security. They trust Ubuntu/Canonical, they trust in their expertise regarding security.
What can be done now?
In the short term, probably only staff from other departments of Canonical can assist to expedite delivery. I still don’t understand the problem - why does it take so much longer than publishing Firefox packages, even of major versions?
What can be done for 22.04?
If sufficient capacities cannot be built up, I see following options as well:
a) Replace debian package with snap package, similar to Chromium and Firefox.
b) Remove Thunderbird debian package from standard repositories. Offer another (better supported) or no preinstalled mail client.
Safety comes first, so it’s better not to offer a debian package at all than an insecure one and let people think they are safe.