What would the Raven Queen want as a Warlock’s patron in D&D 5E?
What the Raven Queen wants is a question for the DM to answer. However, a suggestion on what he may want is another plane (other than this one) where the souls of all life go at death and await judgement to decide whether they are reincarnated.
DMs should also remember that while the Raven Queen does not bear any special animosity towards any particular alignment, she absolutely hates chaotic evil alignments. So if your idea of “good” or “evil” doesn’t match up with what society deems appropriate, I would suggest you find another patron. And summoning spells have been known to draw her attention in very unpleasant ways…so be careful who you use them on!