Change GitHub default branch from master to main

5 simple steps that I tested and used to make the change in under 1 minute.

Point HEAD to main branch

git symbolic-ref refs/remotes/origin/HEAD refs/remotes/origin/main

Change default branch to main on GitHub
- Navigate in your browser to your GitHub repository.
- From the left rail, click Settings -> Branches and change the default branch to main
Delete master branch on the remote repo
```
git push origin --delete master
```

Updating a local clone after a branch name changes

After you rename a branch in a repository on GitHub, any collaborator with a local clone of the repository will need to update the clone.

From the local clone of the repository on a computer, run the following commands to update the name of the default branch.

git branch -m OLD-BRANCH-NAME NEW-BRANCH-NAME
git fetch origin
git branch -u origin/NEW-BRANCH-NAME NEW-BRANCH-NAME
git remote set-head origin -a

Optionally, run the following command to remove tracking references to the old branch name.

git remote prune origin

Source: GitHub: Updating a local clone after a branch name changes

To initialize a new Git repository and set the default branch to main:

git init --initial-branch=main