When I preview it in a browser or view it in Thunkable Live on my iPhone 11, it looks the same. But if I download it to my phone, it appears as though the circular buttons are stretched (height > width):
I tried changing individual buttons’ Resize Mode to cover, contain, stretch or center. The downloaded project still looks exactly like the second screenshot above.
To get a near circle you need to get the ratio between the height and width of the actual screen using computed height and width and then update the component size. This option is, unfortunately, not yet available in DnD.