https://wptips.dev/custom-rest-api - Snippet from that article to create the custom post type

functions.php

<?php

add_action( 'init', 'my_post_types' );

function my_post_types() {
  register_post_type( 'project', [
    'public' => true,
    'label' => 'Project'
  ] );

  register_taxonomy( 'project_category', ['project'], [
    'hierarchical' => true
  ] );
    
  $has_projects = get_posts(['post_type' => 'project']);

  // create 2 placeholder projects
  if( !$has_projects ) {
    wp_insert_post([
      'post_title' => 'Project 1',
      'post_status' => 'publish',
      'post_type' => 'project',
      'post_content' => 'Lorem ipsum dolor sit amet consectetur adipisicing elit.'
    ]);

    wp_insert_post([
      'post_title' => 'Project 2',
      'post_status' => 'publish',
      'post_type' => 'project',
      'post_content' => 'Quibusdam exercitationem ut culpa, tempora ab illum.'
    ]);
  }
}