Iphone11 Pro white balance photograph problem.

I have an iPhone 11pro and I am taking down shot photographs of small objects. I am using the telephoto setting the objects are in focus and sharp (better than my iphone10), but my background has gone grey. I have adjusted the white balance by pressing the screen and making the background on the screen white, however when I look at the image and transfer to my MacBook Pro the background colour has gone to grey.

I had an iphone10 and used this method to get good results. I am not very technical a bit of a point and shoot person but I would be grateful for any help with this.