First, the background of the player was ok (transparent). Then, on 11 august 2021, I noticed it was black in the inventory and light blue in the cloud save menu (I don't have the screenshot of it).

Now the background in the cloud save menu is ok (transparent) but the inventory one is still broken: sometimes is still black and sometimes even white). 

Edit: I found that the black screen is shown when the inventory is opened with the keyboard shortcut, the white one when the inventory is opened with the inventory button in the hotbar.