I asked AI what Einstein would be working on today if he were alive, the result was a predictably rosy scenario of modern physics problems.
However the reality was that Einstein (in his later years) became isolated from physics developments.
This is an educated guess, because we cannot know how Einstein would have reacted to post-1955 developments: Bell’s theorem, quantum information, the Standard Model, inflation, black hole thermodynamics, dark matter/dark energy, gravitational waves, and modern experimental cosmology. The missing information that would most change my answer is whether “today’s Einstein” would retain his later-life philosophical commitments — realism, locality, geometric unification — or adapt them after seeing modern evidence.