By delaying Login until a later stage, I was able to cut the bounce rate from over 50% to 23%.
The Sign in with Github button was replaced with Get started which allows users to try the first chapter without an account. Then if they like it, they can decide to Register.
Feb 4 is the day when I rolled this feature (noon) which explains why it's around 30%.
Screenshot of Bounce Rate over the last 30 days: https://i.imgur.com/9hEeqFe.png