Well The Metamorphosis focuses a lot around isolation, loneliness, and being separated from much of society. Whereas The Stranger, the novel is more focused around absurdity and free will. Both have elements of being distant from others and the world. Thus, how about a title like this: "Forever Anonymous" or "Who am I" or "The World's Stranger"
Both works have an existential theme, so a title like "Alive, but Existentially Alive?" might work. You would then evaluate how Gregor and Mersault are living beings, but that they both are passively accepting of their position in the world, as opposed to making good decisions for how to live their fullest lives.
You might like to use the title "The Outsider" to comment on both of these works. Both Gregor and Mersault are outsiders who find themselves, for different reasons, unable to engage in society meaningfully. Both too meet a grisly end, though for very different reasons. Both texts have powerful comments to make about the lack of meaning in society.
"Displaced and confused" would be a good title. "The Metamorphosis" is about the human experience of being displaced. "The Stranger" has a similar theme, but others are more confused about the protagonist's attitude. You might focus on comparing the reactions of secondary characters to both protagonists.
Will "portrayal of society" and "social expectation" be a good theme? I have already look into it.