Qt: application crashes when using QWidget::show() - c++

Question

I know that this type of problem has been reported before, but the answers weren't helpful to me. This is the code situation:
// main.cpp
#include <QApplication>
#include "game.h"
int main(int argc, char* argv[]) {
QApplication app(argc, argv);
Game game;
game.show();
return app.exec();
}
// game.h
#ifndef GAME_H
#define GAME_H
#include "scene.h"
class Game {
public:
Game();
void show();
private:
GameScene scene;
};
#endif // GAME_H
// scene.h
#ifndef SCENE_H
#define SCENE_H
#include "GraphicsManager.h"
struct GameScene {
static GraphicsManager<MainWindow> window() { return win; }
private:
static GraphicsManager<MainWindow> win;
};
#endif // SCENE_H
// game.cpp
#include "game.h"
Game::Game() {
scene.window().render();
}
void Game::show() {
qDebug() << "crash test before show";
scene.window().view()->show(); // crashes here
qDebug() << "crash test after show";
}
// GraphicsManager.h
#ifndef GRAPHICSMANAGER_H
#define GRAPHICSMANAGER_H
#include <QGraphicsScene>
#include <QGraphicsView> // inherits QWidget
#include <QGraphicsPixmapItem>
#include <QImage>
#include <QBrush>
template <typename T>
struct GraphicsManager {
void render() { static_cast<T*>(this)->render(); }
QGraphicsScene* scene() { return static_cast<T*>(this)->scene(); }
QGraphicsView* view() { return static_cast<T*>(this)->view(); }
};
struct MainWindow :
GraphicsManager<MainWindow> {
void render() {
m_scene = new QGraphicsScene(0, 0, 800, 800);
m_view = new QGraphicsView(m_scene);
m_view->setHorizontalScrollBarPolicy(Qt::ScrollBarAlwaysOff);
m_view->setVerticalScrollBarPolicy(Qt::ScrollBarAlwaysOff);
m_view->setFixedSize(800, 800);
}
QGraphicsScene* scene() { return m_scene; }
QGraphicsView* view() { return m_view; }
private:
QGraphicsScene* m_scene; // raw pointer is used here, since
QGraphicsView* m_view; // they both inherit QObject,
};
#endif // GRAPHICSMANAGER_H
Now admittedly I am very new to Qt in general, so it's possible that I don't understand some of its mechanics. But as you can see in the minimal code example above, I want to try to use CRTP when it comes to the graphics interface module, and according to my tests, everything works fine until the QWidget::show() method is called in Game::show(). Right after that call the application crashes.
The crash report message does not provide any useful information or hints as to why this happened. Does anyone have an idea of what I have done wrong?
EDIT: This is the compiler message:
11:05:06: Running steps for project test3...
11:05:06: Starting: "C:\CMake\bin\cmake.exe" --build C:/a_Skola/Programmeringsmetodik/space_invaders_testsite/build-test3-Desktop_Qt_6_4_1_MinGW_64_bit-Debug --target all
ninja: no work to do.
11:05:06: The process "C:\CMake\bin\cmake.exe" exited normally.
11:05:06: Elapsed time: 00:00.