Sorry for the late comment. I've recently been listening to, and enjoying, The End of the World with Josh Clark. It seems like a really solid and approachable introduction to existential risks. It starts by covering why x-risks might be things that we should be concerned about, and then talks about AI, biosecurity and other possible threats. Includes interviews with Nick Bostrom, Toby Ord, Anders Sandberg, Robin Hanson and others :)