The default window that Bevy spawns is
created by the WindowPlugin.
When you add your DefaultPlugins you can
customize the settings of each plugin with the DefaultPlugins::set method:
use bevy::prelude::*;
fn main() {
let app_window = Some(Window {
title: "Some title other than \"Bevy App\"".into(),
..default()
});
App::new()
.add_plugins(DefaultPlugins.set(WindowPlugin {
primary_window: app_window,
..default()
}))
// .. the rest of your app
.run();
}