register_post_type() Add excerpt ‘supports’ => array(‘title’, ‘editor’, ‘excerpt’),

On custom_post_types.php page created under themes/mu-plugins

<?php

//Create New Post Type Here
function custom_post_types(){
    register_post_type('event', array(
        
        //All this is Front End Page
        //this will rewrite slug from singular to plural when url /events/ instead of /event/
        'rewrite' => array('slug' => 'events'),
        //This will add functionality to the permalink etc
        'has_archive' => true,

        //All this is Admin
        //Make it public
        'public' => true,
        //Add Title Editor and Excerpt to new page
        'supports' => array('title', 'editor', 'excerpt'),
        //Make it be edited on new "Block" gutenmberg conf
        'show_in_rest' => true,        
        //Admin Left Navigation Label here
        'labels' => array(
            //Name of Admin title on Nav
            'name' => 'Events',
            // //Name of Add new on dropdown
            'add_new' => 'Add New Event',            
            // //Name of Add new event when posting
            'add_new_item' => 'Add New Event',
            // 'edit_item' => 'Edit Event',
            // //menu item All Events link
            'all_items' => 'All Events',
            // 'singular_name' => 'Event'
        ),
        //Admin Icon Label
        'menu_icon' => 'dashicons-calendar'

    ));
}
add_action('init', 'custom_post_types');