Well we've noticed the system doesn't always work for all things. Like example the amulet the hidden wizard that "stoled" never showed the MC it's true effects and why that wizard was so interested to it.
Could be the system way of control the narrative again
Honestly I think it's just the author being like "because plot hehe" which is just annoying, it'd be cool if they elaborated or brought up the system not always working which would be cool but I doubt it
At first I was going into as similar too another story called "Stuck in My Sister's Dating Sim" and it plays similar. With the dating sim that person knows the story already while in "How to Refuse the Route" the main character is assential being guided. The fact that characters can notice the system or some unworldly power to some, means this story can go into so many season.
Like just now thinking that the amulet could have probably reduced the system control allowing Ilya to physically effect....so many theories...I've never thought this deep with story......It's fascinating
So the magic system that tells him everything about an item mysteriously doesnt work for a potion? Sure