As always, this release includes the latest bugfixes of 4.13.22. It also fixes the buggy "title" attributes in the downloads content element. If you used one of the {{insert_*::.}}
insert tags in Twig templates and found that redirects didn't work (e.g. if you included a registration module with redirect page via insert tag) - that should work again now.
About Contao 5.1
The first stable version of Contao 5.1 has been released on 15 February 2023 and was the successor of Contao 5.0. 5.1 has been updated until 14 August 2023, after which it has been replaced by Contao 5.2.