No, Albert Einstein did not ultimately find a complete and successful unified field theory or a final explanation for gravity during his lifetime. However, his work laid the foundation for modern theories of gravity and greatly advanced our understanding of the subject.
Einstein is best known for his development of the theory of general relativity, which revolutionized our understanding of gravity. General relativity describes gravity as the curvature of spacetime caused by mass and energy. It successfully explained the motion of objects in the presence of gravitational fields and made several successful predictions, such as the bending of light around massive objects and the existence of gravitational waves.
However, despite his extensive efforts, Einstein was not able to reconcile general relativity with the other fundamental forces of nature, such as electromagnetism and the strong and weak nuclear forces. He spent much of his later years searching for a unified field theory that would encompass all known forces into a single framework. This theory was intended to explain not only gravity but also electromagnetism and the other fundamental forces within a consistent mathematical framework.
Einstein's attempts at a unified field theory, particularly his later work on the "Einstein–Cartan theory" and "unified field theory of gravitation and electromagnetism," did not yield definitive success. He encountered various mathematical and conceptual challenges, and no final theory was achieved during his lifetime.
Since Einstein's time, theoretical physicists have continued to search for a unified theory that can encompass all fundamental forces, including gravity. Prominent attempts at unifying gravity with the other forces include string theory, loop quantum gravity, and various approaches in quantum field theory. However, a complete and experimentally verified unified theory of all the fundamental forces, often referred to as a "theory of everything," remains an open and active area of research in theoretical physics.