For gods sake, how am I able to start the DLC chapter???

I installed most current version 2.2.0.5.
I finished chapter 7 on original/puzzle mode but after credits and epilogue I get dropped to the main menu.
There "Continue" restarts chapter 7.
"Chapter Selection" has only entries from chapter 1 to 7.
"New Game" has no extra entry, only the known difficulty modes. Menu has also no extra entry like "Start DLC".
Only "Gallery" hints for DLC ("Last Chapter: Commitment, [...]").

WTF?! I'm going nuts, trying to find a way to play the DLC... What am I doing wrong???

Please, can anybody help me?

PS: I also tried to manipulate "savegames.ini" and "general.ini" and changed "unlocked_stage" and "current_stage" to "=9.000000" (I took the number from "challenges.ini"), but only Errors appeared in "Chapter Selection" and "Load Game":

ERROR in
action number 1
of Draw Event
for object o_menu_load_preview:

Trying to draw non-existing sprite.
at gml_Object_o_menu_load_preview_Draw_0

Did anyone at all play the DLC?

So I got an answer from the developers:
"Should be accessible by clicking on Liam on the main menu. He's next to the fireplace, left of the screen! Sorry!"

Poor design choice to break their own game control paradigm and to not highlight that in any way. Who would try to click randomly into the background, when before all of the game was selectable through the text buttons on the bottom...