So I went to the Apple Store and to my surprise, they didn´t fix my phone, they gave me some excuses it was not doable to clean it, that maybe it was a problem with the frame, etc.
They gave me a refurbished iPhone X. I inspected it. I took the plastic protection and there was dust on top of the lenses, already pretty weird. I inspected inside and saw dust... 1 particle in each lense, but frontal camera ok.
I told them about it, they saw the dust and after a bit of "chatting", they gave me a second refurbished iphone. Same problem, dust inside, even more than the first refurbished one.
I ended going home with the first refurbished phone, unhappy, after being treated not nicely. I really think Apple doesn't know how to create a properly sealed duo-camera module. Point. For any reason, dust is getting trapped in the factories between camera module and glass. And this doesn't even explain how I had in my initial iPHone X dust in the real camera, inside!
My other iPhone 8 with one lens is pristine, nothing in, same with iphone 6S, 6, 5, 4 and even first iPhone gen 1.
I think the iPhone X has some kind of sealing/design issue. I am pretty sure in some months I will see more dust inside. Hope I am wrong.