I can think of one technology that could easily solve this problem: an ability to “freeze” people into some kind of hibernation indefinitely until they are need

I can think of one technology that could easily solve this problem: an ability to “freeze” people into some kind of hibernation indefinitely until they are needed. Potentially, this could even mean going to sleep on Earth and then waking up on some distant planet colony where they need people. Jarring, but somehow people can find a good life this way I bet.