I’m aware of Debian’s reputation for not having the most up-to-date software in its repository but have just noticed that Thunderbird is on its current version. Which makes me ask:
When does Debian update a package? And how does it decide when to?
I’m particularly interested in when it will make available the upcoming major release of GIMP to 3.0.
Some software is so complex and difficult that Debian does not maintain it on their own, and instead follows the upstream release cycle.
Browsers are one such example, and as you’ve discovered for me, Thunderbird is probably another.
Also, please do not recommend testing for daily usage. It does not receive critical security updates in a timely manner, including for things that would effect desktop users. Use stable, Sid, or another distro. Testing is for testing Debian ONLY, and by using Debian Testing, you are losing the advantage of immediate security fixes that come from literally any other distro.