It’s likely to be your language settings - most of the posts there are tagged ‘Deutsch’, but the first post in your screenshot (with the plane in between the ‘ich’ and the ‘iel’) isn’t (it’s just ‘unspecified’).
If it’s that, you’ll need to add ‘Deutsch’ as a language you understand in your user settings.
programming.dev changed how active users are calculated on their instance to include voters as well as posters & commentators. It’s a massive difference - programming_humor went from about 700 monthly active users to about 7000, for example.
Viewing communities from other instances from programming.dev’s perspective will give a figure that includes voting activity.