Super quick tip here, but probably non-obvious.
If you want to be able to use WordPress’ Gutenberg editor with a Custom Post Type you’ll need to register the post type with REST API support.
'label' => 'Things',
'labels' => ['...'],
'show_in_rest' => true, //required to enable Gutenberg editor
Considering how widely used and how widely extended WordPress is, it’s renowned for its backwards compatibility with new releases. The next major WordPress update – v5.0 – is due for release in a couple of days amid a shroud of hot drama over the stability of the new Gutenberg editor.
Gutenberg is a major redesign in the way Pages and Posts can be constructed within WordPress. It brings the concept of custom ‘Blocks’ which allow chunks of information to be presented in specific ways. Conceptually this approach has widespread support, but retrofitting it into the existing WordPress ecosystem is a challenge. The team have put a lot of effort into backwards compatibility, but it’s a complex process and there are widespread doubts about how smoothly that will go.
Knowing this the WordPress development team have been distributing a WordPress Classic Editor plugin to allow sites to keep the old editor with the new version of WordPress.
My advice would be for anyone updating an existing WordPress site is to first install and activate this plugin, and to only use the new Gutenberg editor once they’ve been able to test it on a staging version of their website. Gutenberg may well work fantastically with your theme and plugins, but it’s far from guaranteed and you don’t want to be trying it out in production!