you have to play the game 2 times the second playthrough in the black gallery you will get to the Exhibit

1st passage of the game

-Read Poster in maze

• do not kick the mannequin and doll head
• talk to Garry 7 times after waking up
• read the milk puzzle
• When in Sketchbook, talk to Garry 6 times at sunlight
• save the game after burning the messes
• complete Memory's Crannies
• load record
• do the Promise of Reunion ending (don't press F12)

2nd Passage of the game

• find The Hanged Ib while hide and seek
• kick the mannequin's head
• Read 'Hanged Garry' poster
• select the 'Are you okey' option after selecting Mary
• Ropes
• kick the doll's head
• save the game before entering the doll room
• end A Painting's Demise (Garry may die in the doll room)
• talk to Mary 8 times then do the ending Welcome To The World Of Guertena
• Once you get both of those endings, use that save file to complete Doll Room and go to Sketchbook
• Make your next save after you get the lighter from Garry

Here it would be best to do 'Forgotten Portrait' first and then revert back to that save to go back and do 'Ib All Alone'

• It makes it easier in the sense that you can save to black gallery and just get that ending faster

• load the record then go to Exhibit

• if you go through the Exhibit, do the ending 'Together, Forever'