@For newbie: Don't forget crack before launching the game (otherwise you will get the "no license" error). By doing one of the following:
Method 1: before installing the game, check the following box:
Method 2: or after installing the game, open the iso file, copy everything in the "RUNE" folder, then paste them to where you installed the game, enjoy ;) (see tutorial image here if you still dont know: https://igg-games.com/how-885614657-to-install-game-and-update.html)
I solved it! If anyone has the same problem with this part, just create another save file in a different slot and select chapter 4 (it takes at most a few minutes to return to where you left off), the entry with the curtain will be open.
The game turned out to be surprisingly..... mediocre. This dev used to be good at telling the story from the environment (not by words), but this time it's a totally nonsensical mess. The janky semi-fixed camera angle and overly dark environment don't help either.
There was supposed to be a passageway in that curtain, but it doesn't work.
If anyone has the same problem with this part, just create another save file in a different slot and select chapter 4 (it takes at most a few minutes to return to where you left off), the entry with the curtain will be open.
https://youtu.be/I3GeAF-QecM