RTX is the latest, so it has more awesome features than GTX. RTX is equipped with Tensor and RT cores. These cores are very meaningful for real-time ray tracing, as well as deep learning supersampling.
GTX card doesn’t have the extra AI and ray-tracing silicon. So, you find the older GTX prefix in older NVIDIA graphic cards. But you don’t worry so much about the quality of GTX. You can still enjoy your game with a GTX card.