EggMUP that registers a demo Custom Post Type and Custom Taxonomy. Edit the arrays to create your own, then drop into your mu-plugins directory.

custom-data-types.inc.php

<?php
/**
 * Plugin Name:     EggMUP: Register Custom Data Types
 * Plugin URI:      https://gist.github.com/ianpegg/
 * Description:     Defines and registers custom post types and custom taxonomies.
 * Version:         1.0.0
 * Author:          Ian Pegg
 * Author URI:      https://eggcupwebdesign.com
 * php version 8.0.28
 *
 * @category   Must_Use_Plugin
 * @package    WordPress_Plugin
 * @author     Ian Pegg <ian@eggcupweb.com>
 * @license    GNU/GPLv3 https://www.gnu.org/licenses/gpl-3.0.txt
 * @link       https://eggcupwebdesign.com
 */

namespace EggCup\MUP\CustomDataTypes;

if (!defined('ABSPATH')) {
    exit;
}

register_deactivation_hook(__FILE__, '\flush_rewrite_rules');
register_activation_hook(__FILE__, __NAMESPACE__ . '\\Register_Custom_Data_types');

/**
 * Register taxonomy first by demoting CPT registration priority:
 * @link https://cnpagency.com/blog/the-right-way-to-do-wordpress-custom-taxonomy-rewrites/
 */
add_action('init', __NAMESPACE__ . '\\Register_Custom_taxonomies', 10);
add_action('init', __NAMESPACE__ . '\\Register_Custom_Post_types', 11);


function Register_Custom_Data_types()
{
    /**
     * Call the custom data type registration functions here.
     * These functions should also be hooked into 'init'.
     */
    Register_Custom_taxonomies();
    Register_Custom_Post_types();
    flush_rewrite_rules();
}


function Register_Custom_Post_types()
{
    /**
     * Initialise a new array to store all of our CPT definitions:
     **/
    $Arr_cpt_definitions = [];

    /**
     * Define each CPT in a new array:
     **/
    $Arr_cpt_definitions[] = [
        'Str_cpt_name'  => 'projects',
        'Arr_args' => [
            'label' => esc_html__('Projects', 'eggmup'),
            'labels' => [
                'name' => esc_html__('Projects', 'eggmup'),
                'singular_name' => esc_html__('Projects', 'eggmup'),
                'menu_name' => esc_html__('Projects', 'eggmup'),
                'all_items' => esc_html__('All Projects', 'eggmup'),
                'add_new' => esc_html__('Add new', 'eggmup'),
                'add_new_item' => esc_html__('Add new Project', 'eggmup'),
                'edit_item' => esc_html__('Edit Project', 'eggmup'),
                'new_item' => esc_html__('New Project', 'eggmup'),
                'view_item' => esc_html__('View Project', 'eggmup'),
                'view_items' => esc_html__('View Projects', 'eggmup'),
                'search_items' => esc_html__('Search Projects', 'eggmup'),
                'not_found' => esc_html__('No Projects found', 'eggmup'),
                'not_found_in_trash' => esc_html__('No Projects found in bin', 'eggmup'),
                'parent' => esc_html__('Parent Project:', 'eggmup'),
                'featured_image' => esc_html__('Featured image for this Project', 'eggmup'),
                'set_featured_image' => esc_html__('Set featured image for this Project', 'eggmup'),
                'remove_featured_image' => esc_html__('Remove featured image for this Project', 'eggmup'),
                'use_featured_image' => esc_html__('Use as featured image for this Project', 'eggmup'),
                'archives' => esc_html__('Project archives', 'eggmup'),
                'insert_into_item' => esc_html__('Insert into Project', 'eggmup'),
                'uploaded_to_this_item' => esc_html__('Upload to this Project', 'eggmup'),
                'filter_items_list' => esc_html__('Filter Project list', 'eggmup'),
                'items_list_navigation' => esc_html__('Project list navigation', 'eggmup'),
                'items_list' => esc_html__('Projects Project list', 'eggmup'),
                'attributes' => esc_html__('Project attributes', 'eggmup'),
                'name_admin_bar' => esc_html__('Projects', 'eggmup'),
                'item_published' => esc_html__('Project published', 'eggmup'),
                'item_published_privately' => esc_html__('Project published privately', 'eggmup'),
                'item_reverted_to_draft' => esc_html__('Project reverted to draft', 'eggmup'),
                'item_scheduled' => esc_html__('Project scheduled', 'eggmup'),
                'item_updated' => esc_html__('Project updated', 'eggmup'),
                'parent_item_colon' => esc_html__('Parent Project:', 'eggmup'),
            ],
            'description' => '',
            'public' => true,
            'publicly_queryable' => true,
            'show_ui' => true,
            'show_in_rest' => true,
            'rest_base' => '',
            'rest_controller_class' => 'WP_REST_Posts_Controller',
            'has_archive' => true,
            'show_in_menu' => true,
            'show_in_nav_menus' => true,
            'delete_with_user' => false,
            'exclude_from_search' => false,
            'capability_type' => 'post',
            'map_meta_cap' => true,
            'hierarchical' => false,
            'rewrite' => [
                'slug' => 'projects',
                'with_front' => false
            ],
            'query_var' => true,
            'menu_position' => 7,
            'menu_icon' => 'dashicons-portfolio',
            'supports' => [
                'title',
                'editor',
                'thumbnail',
                'excerpt',
                'revisions',
                'author'
            ],
            'taxonomies' => [
                'services'
            ],
        ],
    ];

    /**
     * Spin over all of our CPT definitions and register them using WP API:
     **/
    if (!empty($Arr_cpt_definitions)) {
        foreach ($Arr_cpt_definitions as $Arr_cpt) {
            register_post_type(
                $Arr_cpt[ 'Str_cpt_name' ],
                $Arr_cpt[ 'Arr_args' ]
            );
        }
    }
}


function Register_Custom_taxonomies()
{
    /**
     * Initialise a new array to store all of our Taxonomy definitions:
     **/
    $Arr_taxonomy_definitions = [];

    $Arr_taxonomy_definitions[] = [
        'Str_tx_name' => 'services',
        'Str_assoc_cpt' => [
            'projects'
        ],
        'Arr_args' => [
            'label' => esc_html__('Services', 'eggmup'),
            'labels' => [
                'name' => esc_html__('Services', 'eggmup'),
                'singular_name' => esc_html__('Service', 'eggmup'),
                'menu_name' => esc_html__('Services', 'eggmup'),
                'all_items' => esc_html__('All Services', 'eggmup'),
                'edit_item' => esc_html__('Edit Service', 'eggmup'),
                'view_item' => esc_html__('View Service', 'eggmup'),
                'update_item' => esc_html__('Update Service name', 'eggmup'),
                'add_new_item' => esc_html__('Add new Service', 'eggmup'),
                'new_item_name' => esc_html__('New Service name', 'eggmup'),
                'parent_item' => esc_html__('Parent Service', 'eggmup'),
                'parent_item_colon' => esc_html__('Parent Service:', 'eggmup'),
                'search_items' => esc_html__('Search Services', 'eggmup'),
                'popular_items' => esc_html__('Popular Services', 'eggmup'),
                'separate_items_with_commas' => esc_html__('Separate Services with commas', 'eggmup'),
                'add_or_remove_items' => esc_html__('Add or remove Services', 'eggmup'),
                'choose_from_most_used' => esc_html__('Choose from the most used Services', 'eggmup'),
                'not_found' => esc_html__('No Services found', 'eggmup'),
                'no_terms' => esc_html__('No Services', 'eggmup'),
                'items_list_navigation' => esc_html__('Services list navigation', 'eggmup'),
                'items_list' => esc_html__('Services list', 'eggmup'),
            ],
            'public' => true,
            'publicly_queryable' => true,
            'hierarchical' => true,
            'show_ui' => true,
            'show_in_menu' => true,
            'show_in_nav_menus' => true,
            'query_var' => true,
            'rewrite' => [
                'slug' => 'services',
                'with_front' => false,
                'hierarchical' => true,
            ],
            'show_admin_column' => true,
            'show_in_rest' => true,
            'rest_base' => 'services',
            'rest_controller_class' => 'WP_REST_Terms_Controller',
            'show_in_quick_edit' => true,
        ],
    ];

    /**
     * Spin over all of our taxonomy definitions and register them using WP API:
     **/
    if (!empty($Arr_taxonomy_definitions)) {
        foreach ($Arr_taxonomy_definitions as $Arr_taxonomy) {
            register_taxonomy(
                $Arr_taxonomy[ 'Str_tx_name' ],
                $Arr_taxonomy[ 'Str_assoc_cpt' ],
                $Arr_taxonomy[ 'Arr_args' ]
            );
        }
    }
}