This functions correctly when classic editor is installed and enabled, so we'd need to investigate the original code and update it so that it shows in Gutenberg as well.
Examples & info from Jarrett: Sure -- go into any Edit Post and look down the right rail: between Tags and Post Types is Neighborhoods: http://citylimits-archive.flywheelsites.com/wp-admin/post.php?post=5629648&action=edit ... here's a screenshot: https://drive.google.com/file/d/1FL58gXmNLJprlwprAaualx_9xwPZX1Ik/view?usp=sharing
Log time in Everhour city limits covered support.