C++ ::  how To Handle Async Operations

I've been thinking over this for long time... For example, when a button is clicked, print a string "clicked" after 5 seconds. (the button won't be blocked)

Thread should be the only way to do this:

btn.on_click = []() {
thread thrd([]() { sleep_5_seconds(); cout << "clicked" << endl; });
thrd.start();
};

the local variable thrd is destructed right after it starts, which may cause a crash, so use new operator:

btn.on_click = []() {
thread* thrd = new thread([]() { sleep_5_seconds << "clicked" << endl; });
thrd->start();
};

The thrd never get deleted

How would you solve problem like this?