The most reliable "fix" is now built directly into the game. On , developer Iron Galaxy released a major update (Patch 1.3.20812) that officially removed the AVX2 restriction.
While the game is now playable on older CPUs, reviewers have noted that performance is generally better when the game is GPU-bound, though some users report a smooth experience even on decade-old processors. How to Apply the Fix Update via Steam/Epic: uncharted 4 avx2 fix new