Not that many people use Copilot Chat, anecdotally. We've focused on codebase chat when building Cody (https://cody.dev), since we can use a lot of the code search stuff we've built before. It's hard to build, esp. cross-repo where you can't just rely on what's accessible to your editor. You can try it on the web if you sign up and then go to any repository's sidebar on https://sourcegraph.com/search, or get it for VS Code/JetBrains/etc.