I tried an upgrade from 2.4.24 to 2.5.3 on a staging site ( https://kigges.hwolf.de/ )
After this the upgrade script was ok, but now all date strings a strange like this:
Forumszeit: %02.%08.%2022, %12:%Aug (Europe/Berlin)
Allgemeine Termine - holger, %09.%11.%2018, %13:%Nov […] [*] [○] [x] (Rund um Fußball)
It's with also with the default theme.
This has nothing to do with the theme in itself. The date format is defined in the language file. For gernam language these are the lines 17 and 18 in lang/german.lang.
How I searched for the cause:
In the version 20220529.1 the single entry page uses the key
time_format_full to format the time. That does it since ages. But because of the deprecation of the function
strftime we moved to the PHP-function
date with the first version of the 2.5-branch, which was 20220508.1.
For comparision reasons:
strftime wanted the (german) full date format in the format
%A, %d.%m.%Y, %H:%M, the function
date wants it as
l, d.m.Y, H:i. And that differennce tells me, that you forgot to upload the language files (at least) for the new version.
Trenne niemals Müll, denn er hat nur eine Silbe!