Not sure if it's a recent change since I ended up here because I could not find the chat either, but you can open the chat with ⌃⌘I

here's the official doc
https://code.visualstudio.com/docs/copilot/getting-started#:~:text=Open%20the%20Chat%20view%20from%20the%20Copilot%20menu%20in%20the%20title%20bar%20or%20press%20%E2%8C%83%E2%8C%98I.