The potion results in an ending, so dont drink that if you want to progress. For the shamans task you have to go to the room west of where the shaman is. There you can get the item needed to progress.
I saved this file. After receiving the task, I entered the room on the left. There was a mantis and a werewolf in it. The werewolf would ask me the purpose of coming here. I answered him truthfully. He asked me to look for it freely, but I didn't find what the shaman wanted in this room. Is there a bug in my game? Or what is it specifically?
If that is an option for you, then you might try it. That's up to you. I am sorry you are having trouble with the game, but I am not sure how I am able to provide any help. This bug has not been reported before as far as I know and I cannot provide any support for the chinese version of the game, I am sorry.
(I'm gonna laugh at my stupidity.)The sample should be taken from the table on the left, where there are a few glasses of milk. Before, I always interacted with other locations, so I didn't find what I was really looking for. Then I searched for a long time on the table on the right. After reading your comment, I decided to look for it carefully. Now I realize that I am so stupid, hahahaha