No, the fact that we can see galaxies that are 12 billion light years away does not mean that the universe has already ended. The statement that the universe will end in 5 billion years is likely referring to a prediction about the future evolution of the universe based on current scientific understanding.
When we observe objects that are very far away, we are actually seeing them as they were in the past because the light from those objects takes time to reach us. This is because the speed of light is finite, and it takes time for light to travel across vast cosmic distances. So, when we observe a galaxy that is 12 billion light years away, we are seeing it as it was 12 billion years ago.
The age of the universe is estimated to be about 13.8 billion years, so the light we receive from objects that are 12 billion light years away is from a time relatively close to the beginning of the universe. It does not mean that the universe has already ended. There is still a vast amount of time ahead before the predicted end of the universe, and we are currently observing objects that existed in the early stages of its history.
It's worth noting that the prediction about the end of the universe is based on our current understanding of cosmology and is subject to refinement as our knowledge advances. The ultimate fate of the universe is still an active area of research and speculation among scientists.