If you are working with vector font, you can set some global settings that should help.
In Project Settings, tick Advanced Settings and then look for:
General -> Rendering -> Textures -> Canvas Textures -> Default Texture Filter: set to Nearest
General -> GUI -> Theme -> Default Theme Scale: set to the appropriate value, e.g., 4
Note that in this same panel you can set the default theme to your own. Then, as suggested, reload the project for the changes to apply.
If you are working with bitmap fonts, then yes, you have to manually scale the root Control node of all your scenes, while still enabling the texture filter to nearest. But there should be few of them hopefully.
Though, I'm not an expert, so there might be a better way.

