What does it mean to say God “will not again curse the ground any more for man’s sake” (Gen 8:21)?

Let us be clear that he is quite specifically talking about the ground.He is not saying he will never again curse man. Rather, he is saying he will not give any further curse of the ground—of the sort given to Adam, then to Cain, and then to the whole of humanity in the Flood—i.e., the ground from which man lives. The remark, “I will never again destroy every living thing,” extends the promise of clemency. Moreover, the short poem of 8:22 I believe elaborates the meaning of “curse the ground,” by saying that the sunny days and the seasons of planting and harvest will continue; that would seem to undo Cain’s curse in particular, thus making it possible for all men to engage in farming again (though some, like Nebuchadnezzar, would be specifically cursed to engage in nothing but hunting and gathering). But we continue to live under Adam’s curse of the ground, which yields its fruits only after much toil; as Paul says, “the whole creation groaneth and travaileth in pain” (Rom 8:22).