No need to install the gallery mod to see that scene, just edit the save file a little.
After you chose Z-choice - 2 people and completed Ann's quest, even fucked her, edit the variable 0087 so it will be >=3 (you can gain option to peek from the window to see the scene), or >=5 (you will gain additional option to interact with the door, though it's just 1 line from MC: "I...shouldn't walk in on them.")
View attachment 3725419
Remember to save before checking the room, because you wont be able to replay that scene later.