It is very easy to start building a Drupal 9 website in your local once you have got a few things right. Since composer is a recommended way to use Drupal, I have mentioned instructions for a composer-based setup. Here are the steps along with relevant links to help you quickly set things up.
1. Install MAMP or MAMP Pro in your system (https://www.mamp.info/en/mac/)
2. Install composer and command-line PHP in your system. (https://getcomposer.org/download/, https://www.php.net/manual/en/install.macosx.php). You can also use the MAMP provided PHP in your CLI by checking the following link https://www.choosepizzi.net/mamp-lets-make-terminal-use-mamps-php-instead-of-macs-version/.
3. Download the zip file of the latest release from this page https://github.com/drupal/recommended-project/tags.
4. Extract the content of the zip file to a folder let's say Drupal9 and place that folder in this directory /Applications/MAMP/htdocs/.
5. Go to the terminal and change your directory to '/Applications/MAMP/htdocs/' and run command composer install. This will download the latest code as well as all the dependencies. The codebase fro Drupal is placed in the 'web' directory.
6. Configure the VHost settings as per this blog post https://medium.com/@wilbo/adding-a-virtual-host-in-mamp-for-mac-a6c717cc0475. Make sure it is configured in such a way that the 'web' folder is the root of your application.
7. Hit the configured URL from the browser and install Drupal.