Assuming that in the future most jobs will be replaced by artificial intelligence or other advanced systems, is it (in your opinion) highly likely that the powerful figures of this world would want to commit genocide against a large part of the world’s population, or would we be dealing with true philanthropists?
You don’t need to actively kill people off unless you’re in a rush. Just let climate change render parts of the world uninhabitable while enforcing strict border control, and make sure your population don’t have access to decent healthcare and vaccinations so that prevmtable diseases reduce the local numbers.