After creating a repo on GH:

gistfile1.md

Create a new repository on the command line

echo "# <app-name>" >> README.md
git init
git add README.md
git commit -m "first commit"
git branch -M main
git remote add origin git@github.com:<username>/<repo>.git //<-- using SSH key
git push -u origin main

…or push an existing repository from the command line

git remote add origin git@github.com:<username>/<repo>.git //<-- using SSH key
git branch -M main
git push -u origin main