The Thunderbird folks are somewhat unpredictable. For 140.3.0 they made their build on a Thursday to be release on Tuesday the following week. Today is Saturday, and they haven't done 140.3.1 yet which is due on Tuesday. Well, "due" is in the eye of the beholder, looks like the old "volunteer spirit" before 2020 with the motto "Ship when ready" is still alive, even with ~50 paid staff and a multi-million dollar turnover. Likely they'll do it on Monday in a hurry. They're already earmarked 12 bugs for backport to ESR 140, but the backport hasn't happened yet.
Meanwhile we've added more fixes to Betterbird, which will ship in 140.3.1, and which are already available in the "latest build" versions for users who want to try them out early. As always, the Release Notes have the full detail. Amongst the goodies, we're fixing a couple of regressions: disappearing linebreaks when editing mailcites, and OWL default accounts losing their default status. We're also brushing off a fix to the "Junk" button whose context sensitivity was lost in the 2023 Supernova-Kaboom. The Thunderbird folks walked away from a 95% complete solution in February 2025.