The game is suitable for all mobile phone screen sizes

I searched in forum topics to make the game fit all phone screens, but the attempts were unsuccessful.
I am creating a game with a vertical orientation of 720 and a height of 1280, with the option activated. The size of the game does not change, but it does not fit all phones when tested, so there remains a lot of space on some phones that are not covered by the game screen. When the option to fit the aspect ratio or screen size is activated, the game appears in the middle of the screen only. How do I deal with this issue?