Create a custom WordPress post type to keep your ideas in one place.

The following example will create Ideas menu entry where you can jot down your ideas.
The whole process is really fun.

<?php
/**
 * Plugin Name:       Ideas
 * Plugin URI:        https://github.com/milosz/wp-ideas
 * Description:       Ideas
 * Version:           0.4.0
 * Requires at least: 5.8
 * Requires PHP:      7.4
 * Author:            Milosz Galazka
 * Author URI:        https://sleeplessbeastie.eu
 * License:           GPL v2 or later
 * License URI:       https://www.gnu.org/licenses/gpl-2.0.html
 */

namespace Ideas;

// Register Tags
function taxonomy_tags() {
	$labels = array(
		'name'                       => __('Tags'),
		'singular_name'              => __('Tag'),
	);
	$args = array(
		'labels'                     => $labels,
		'hierarchical'               => false,

		'public'                     => false,
		'publicly_queryable'         => false,

		'show_ui'                    => true,
		'show_in_menu'               => true,
		'show_in_nav_menus'          => false,
		'show_in_rest'               => false,
		'show_tagcloud'              => false,
		'show_in_quick_edit'         => false,

		'show_admin_column'          => true,

		'query_var'                  => false,
	);
	register_taxonomy('ideas_tags', 'idea', $args);

}
add_action('init', __NAMESPACE__ . '\taxonomy_tags', 0);

// Register Categories
function taxonomy_categories() {
	$labels = array(
		'name'                       => __('Categories'),
		'singular_name'              => __('Category'),
	);
	$args = array(
		'labels'                     => $labels,
		'hierarchical'               => true,

		'public'                     => false,
		'publicly_queryable'         => false,

		'show_ui'                    => true,
		'show_in_menu'               => true,
		'show_in_nav_menus'          => false,
		'show_in_rest'               => false,
		'show_tagcloud'              => false,
		'show_in_quick_edit'         => false,

		'show_admin_column'          => true,

		'query_var'                  => false,
	);
	register_taxonomy('ideas_categories', 'idea', $args);

}
add_action('init', __NAMESPACE__ . '\taxonomy_categories', 0);

// Register My ideas post type
function create_post_type() {
	$labels = array(
		'name'                  => __('Ideas'),
		'singular_name'         => __('Idea'),
	);

	$capabilities = array(
		'edit_post'              => 'administrator',
		'read_post'              => 'administrator',
		'delete_post'            => 'administrator',

		'edit_posts'             => 'administrator',
		'edit_others_posts'      => 'administrator',
		'publish_posts'          => 'administrator',
		'read_private_posts'     => 'administrator',
	);

	$args = array(
		'labels'                => $labels,

		'public'                => false,
		'exclude_from_search'   => true,
		'publicly_queryable'    => false,

		'hierarchical'          => false,

		'show_ui'               => true,
		'show_in_menu'          => true,
		'show_in_nav_menus'     => false,
		'show_in_admin_bar'     => false,
		'show_in_rest'          => false,

		'menu_position'         => 4,
		'menu_icon'             => 'dashicons-lightbulb',

		'supports'              => array('title', 'editor'),
		'taxonomies'            => array('ideas_categories', 'ideas_tags'),

		'has_archive'           => false,

		'rewrite'               => false,

		'query_var'             => false,

		'can_export'            => true,

		'delete_with_user'     => false,

		'capabilities'         => $capabilities,
	);
	register_post_type('idea', $args);

}
add_action('init', __NAMESPACE__ . '\create_post_type', 0);

// Set every My Idea to private
add_filter('wp_insert_post_data', function($post) {
	if( $post['post_type'] == 'idea' && $post['post_status'] != 'trash') $post['post_status'] = 'private';
	return $post;
});

// Disable rich editor
add_filter('user_can_richedit', function($default) {
	if( get_post_type() == 'idea') return false;
	return $default;
});

Source code of this simple but very uplifting plugin is available at GitHub: milosz/wp-ideas.

ko-fi