Welcome to the forum.
The white thing you see is a stick on “shield”. It should of come attached. People often find them in their poop collectors and ask about them. Some people have theorized it’s to help stop filament sticking to the side of the poop shoot or that it is a heat shield.
The fact that your X1C doesn’t seem to have it isn’t something I would be overly concerned about. The X1C development is ever ongoing and Bambu may not be adding them on the newest machines. Either way you can submit a customer support ticket to see what they have to say.