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.
it usually updates most packages when a new patch version is released (eg 2.3.1 -> 2.3.2). besides that, they will not update packages to new releases that add features
there are some special cases where it might choose to update more often. debian uses firefox esr by default, but it will update to a newer esr version no matter what, for security reasons. the same must be true for thunderbird.