NotSupportedError in Django project using AWS App Runner

It looks like Django still thinks you're trying to use the default sqlite3 DB. Can you verify the "DATABASES" variable in settings.py is configured with the postgres connection string?

DATABASES = {
    "default": {
        "ENGINE": "django.db.backends.postgresql",
        "NAME": "mydatabase",
        "USER": "mydatabaseuser",
        "PASSWORD": "mypassword",
        "HOST": "127.0.0.1",
        "PORT": "5432",
    }
}

You can also check against this tutorial on deploying Django to AppRunner, postgres is covered near the middle.