He's been called one of the church fathers of antisemitism, and people have drawn a line from his writings all the way to the Holocaust. But early on he condemned cruelty towards the Jewish people as unchristian. So what happened?
u/sunagainstgold has provided an answer to a very similar question to yours before in this thread
She also covered the same question - with the same answer here - but there are also useful discussions in the comments.
Life long Lutheran here. Over the years it's become clear Luther's calling to "Reform" the Catholic Church was corrupted by Melanchthon’s, the Aristocracy's and Royalty's desire to have a simple Ecumenical reformation alongside Calvanism. Clearly early on Melanchthon was Luthers loyal scribe. Not later. No where is this more evident than the Confessions which I've evolved to reject Luther's God given calling . Luther's writings were efficient in meaning and grammar. He was exceptionally erudite without being pedantic. That Melanchthon had to significantly edit the confessions or write an apology is laughable. His treatise on the 53rd Psalm, his Works on Romans or Matthew, Word, Doctrine and Confession and a flood of work on civil government not being a source of righteousness clearly were not written by someone who wrote the confessions and apology or antisemitism as in subsequent writings ascribed to him. I place these false claims and assumptions clearly at the feet of Melanchthon and his disgraceful misrepresentations in Luther's name and clawing his way to self importance.
Forgive my pithiness. Emphasis often needs to offensive to be effective.