Creating pub/sub to ROS2 node spinning in a thread

edit

First of all thank you for ur help ^_^

I've just attached this snippet because I thought it would be the important part as the rest isn't relevant to the problem of the sub/pub only being created inside the thread function, here's the ROSOMNeT.hfile where I declare everything if it helps

class ROSOMNeT
 {
public:

     ROSOMNeT();
    ~ROSOMNeT();

    static ROSOMNeT &getInstance();
    void topic_callback(const std_msgs::msg::String::SharedPtr msg);
    void runROSNode();
    void runSimulation(string configFileName);
    void stopROS();
    rclcpp::Node::SharedPtr &getROSNode();


private:
    static ROSOMNeT instance;

    std::string configFileName;

    rclcpp::Node::SharedPtr rosNode ;

    thread* rosThread;
    void rosMain();
};

As for init ROS in my main I've tried doing that but it didn't change anything so I figured that's not the problem ? (still kept the spin in the thread because I don't want the rest of the code to stop excusing like in the Pub/Sub tutorial) here's how the main look :

    cout << "Starting ROS node" << endl;
    rclcpp::init(argc, argv);
    rosomnet.runROSNode();

the imu sensor looks interesting as it seems like they are creating pub/sub to their node in different classes (which is basically what I'm trying to accomplish) but I still can't figure out how their implementation works impl_ sdf::ElementPtr _sdf ? (seems a bit complicated at my lvl tbh)

Any extra help will be appreciated

EDIT: to address your update:

the way the object was created in main (this already existed on the project so I didn't modify it ) :

cout << "ROSOMNeT++ starting up" << endl;
ROSOMNeT &rosomnet = ROSOMNeT::getInstance()

the getInstance is declared in the ROSOMNeT class :

ROSOMNeT ROSOMNeT::instance;
ROSOMNeT& ROSOMNeT::getInstance() {
   return instance;
  }

The reason why I don't spin the object as they did in the tutorial is because that way the code will stop executing and stay on the spin() command, while I want the node to spin and the rest of the code keep executing so ideally I would call runROSNode() that creates my node, then creates a new thread, that thread does the spin and the rest of the code where I have my pub/sub, callbacks & other code to keep working (I added the creating of pub/sub in rosMain() and runROSNode() to highlight the problem of the pub/sub outside of rosMain() not working ... so if I can eventually create them in runROSNode() I can create them in the other cpp files too )

I was also thinking that the problem comes from the way the node is spinning but I can't figure out why/how to fix it, as this same approach was working with ROS 🤔🤔