You can now sign up using the “Sign-in options” link on the Azure sign-in page.
When you, as a GitHub user, first sign into a Microsoft product with your credentials, GitHub will ask for your permission to consent.
GitHub will share with Microsoft the name and public and private email addresses on your GitHub account to check if you already have a Microsoft account.
If it looks like you already have an account, you will have the option to use that account and add your GitHub account as a login method.
Otherwise, a new account will be created and linked to the GitHub account.