When gaming was young, games were rarely designed for multiple systems at once. When that started, people had to check every screen resolution worked. When phones started coming in many different shapes and sizes, this soon became impractical, and even impossible for most of us. Godot has a way to combat this, of course. But screen size is not your only problem.
Go to ProjectSettings, and find Display -> Window. Go to the bottom of the area on the right, and under "Stretch", there are 3 settings: Mode, Aspect and Shrink.
Modes
Mode
About
disabled
Deafult. Does not stretch the screen.
2d
Only works on 2D, ignores 3D. Streches the 2D world.
viewport
Always works. Stretches the picture.
Aspect
Value
About
ignore
Simply stretches or shrinks the screen.
keep
The image scales, but the aspect ratio never changes. May create black bars around the edge of the screen.
keep_width
Height changes freely, width stays same size as the image scales. Aspect ratio never changes.
keep_height
Width changes freely, height stays same size as the image scales. Aspect ratio never changes.
expand
Scales image to show at minimum of the camera size. May reveal more of the game world vertically if the window is shrank horizontally and vice versa.
As the Shrink value gets bigger, the screen resolution goes down.
The ProjectSetting Rendering -> Quality -> Dynamic Fonts -> Use Oversampling only works when using "Keep Height"/"Keep Width"/"Expand" aspect ratios, and does not work with the "Viewport" Stretch mode.
