可以使用Bevy窗口事件监听器来控制窗口的可见性。具体做法是：

1. 使用WindowCreated事件监听器创建窗口后立即隐藏窗口。

use bevy::prelude::*;

fn main() {
    let mut app = App::build();
    app.add_plugins(DefaultPlugins);

    app.add_event::();

    app.add_startup_system(hide_window_system.system().after(StartupStage::Window));

    app.run();
}

fn hide_window_system(mut windows: ResMut, window_events: Res>) {
    if let Some(window_created_events) = window_events.iter().next() {
        if let Some(window) = windows.get_window(window_created_events.id) {
            window.set_visible(false);
        }
    }
}

2. 在游戏启动完成后再次将窗口恢复可见性。

use bevy::prelude::*;

fn main() {
    let mut app = App::build();
    app.add_plugins(DefaultPlugins);

    app.add_system_set(
        SystemSet::on_update(AppState::Playing)
            .with_system(show_window_system.system())
    );

    app.run();
}

fn show_window_system(mut windows: ResMut, time: Res, state: Res>) {
    if state.current() == &AppState::Playing {
        if let Some(window) = windows.get_primary_mut() {
            if !window.visible() {
                window.set_visible(true);
            }
        }
    }
}

3. 在游戏切换状态时添加状态管理器AppState。

use bevy::prelude::*;

#[derive(Debug, Clone, PartialEq, Eq, Hash)]
enum AppState {
    Loading,
    Playing,
}

fn main() {
    let mut app = App::build();
    app.add_plugins(DefaultPlugins);

    app.init_resource::();
    
    app.add_system_set(
        SystemSet::on_enter(AppState::Playing)
            .with_system(show_window_system.system())
    );

    app.run();
}

至此，我们就完成了在Bevy中启动游戏时隐藏窗口的操作。