We've shipped Betterbird 140.13.0esr-bb25 today. Please refer to the Release Notes for full details.
The Thunderbird had quite some trouble while building the release as mentioned in this earlier article. In fact, as they forgot to update the version number, their first successful build, not mentioning about eight failed builds, was built as 140.12.1/build2. Go figure. Three builds later they finally produced a correct build. However, the underlying Gecko version is already at 140.14.0, which could potentially affect some add-ons which are configured to only function to version 140.13.0.
Back to the Betterbird release. This release contains fixes some important bugs:
Zooming of images in links is back, after being removed from version 140.12.0, but this time controlled via preference mail.allow_zooming_image_links.
Spellcheck now works when the desired languages are stored in preference spellchecker.dictionary as a comma-separated list, for example: en-US,de,es-ES.
As mentioned, full details in the Release Notes.