I have completed "The Dark Eye: Chains of Satinav" twice, got all the Steam achievements. Even the "Endurance" achievement. However, the last 4 videos in the "Extras" section were still locked for me. Also 2 pictures (#6 and #7) were locked for me too. When I hover the cursor over them, it says "Not Unlocked".


I didn't find any information about this either on the Steam forums, or on the Daedalic official website, or on third-party gaming websites. There were only 2-3 created topics where some other players only asked similar questions, but there were no answers there. There weren't even hypotheses from the players about how this content can be unlocked, except that this may be just a bug.

So, I wrote an e-mail to the Daedalic Support Team. And they provided me a detailed answer! For which I am grateful to them.
Then I decided to share the information I received with everyone who likes this game too and who also has questions about the unlocked content after beating the game.

{From the 1st email}

Thank you for reaching out to us and sorry for the long delay in our answer. Sadly it took us quite long to find the answer concerning the pictures, since we had to dig through the source files of the game.

The last 4 spots on the second video page are always empty (if they would contain videos that are still locked they would be displayed similar to the pictures that are still locked), since each page has 9 spots, while the game only contains 13 longer videos and the credits. That these 4 spots show "Not unlocked" when you hover over them is a bug.
Aside from these 13 longer videos there are also 12 very short videos in the game (10 cutscenes and the 2 logos you can see when you start the game), which are not included in the "Extras" section, since they are only between 5 and 20 seconds long. So in total the game contains 25 videos, which you can all find as mkv files in two different resolutions (1920x1080 px and 1024x576 px) in the "videos" folder of the game.

Picture 6 and 7 can sadly not be unlocked for now, so until we fix this bug (it's not yet clear when, because the game is already more than 10 years old so it's not longer in active development and it's also unclear in which situation these images should have been unlocked, since it seems that unlocking them was never implemented) you have unlocked every picture that can be unlocked.

***********************************************************************
{From the 2nd email}

We also added two entries to the game FAQ on our support page
https://www.daedalicsupport.com/en/games/the-dark-eye-chains-of-satinav/?open=collapse44-4 for the pictures and
https://www.daedalicsupport.com/en/games/the-dark-eye-chains-of-satinav/?open=collapse44-5 for the videos (which additionally includes the information that the "Not unlocked" mouseover text for the empty spots on the second video page is fixed in the Switch version of the game) which you can also link.