You can probably do the same things with both, but Flutter is more geared toward applications, where Dear ImGui is more about putting GUIs in places where the GUI is secondary, such as games, creative tools and other graphic-heavy apps.
Here's what Dear ImGui's readme [1] says:
> Dear ImGui is designed to enable fast iterations and to empower programmers to create content creation tools and visualization / debug tools (as opposed to UI for the average end-user). It favors simplicity and productivity toward this goal, and lacks certain features normally found in more high-level libraries.
> Dear ImGui is particularly suited to integration in games engine (for tooling), real-time 3D applications, fullscreen applications, embedded applications, or any applications on consoles platforms where operating system features are non-standard.
Basically: I wouldn't put Flutter inside a graphics heavy video game. I also wouldn't use ImGui for a social mobile app, or something like a business app that requires accessibility.
Here's what Dear ImGui's readme [1] says:
> Dear ImGui is designed to enable fast iterations and to empower programmers to create content creation tools and visualization / debug tools (as opposed to UI for the average end-user). It favors simplicity and productivity toward this goal, and lacks certain features normally found in more high-level libraries.
> Dear ImGui is particularly suited to integration in games engine (for tooling), real-time 3D applications, fullscreen applications, embedded applications, or any applications on consoles platforms where operating system features are non-standard.
Basically: I wouldn't put Flutter inside a graphics heavy video game. I also wouldn't use ImGui for a social mobile app, or something like a business app that requires accessibility.
[1] https://github.com/ocornut/imgui