borg 1.4 is kind of a refreshed 1.2 with mostly the same features and behaviour, but a few bigger changes that could introduce issues and thus were not suitable for just releasing them as 1.2.x, but rather needed some testing first.

Long changelog:

https://borgbackup.readthedocs.io/en/1.4.0/changes.html#version-1-4-0-2024-07-03

Short borg 1.4 overview (from a borg 1.2 perspective):

https://www.borgbackup.org/releases/borg-1.4.html