Gutenberg compatibility for custom metabox location

Description

For some time we have rendered a custom "metabox location" called "acf_after_title". As the name suggests, this location is rendered after the title, and before the WP content editor. Many developers use this location rather than "normal" or "side" to customize the UI with field order that better reflects the front-end. For example, someone may create a field called "Sub Title" and render this after the title and before the content.

To do this, we hook into the "edit_form_after_title" action and render our metabox location via do_meta_boxes().

Issues

• The action "edit_form_after_title" no longer allows us to render HTML after the title in Gutenberg.
• All field groups using this location (and any field group that has been re-arranged into this location) no longer render.

Questions

• What solutions are there to render a custom metabox location?

Start by tracing the existing edit_form_after_title action and do_meta_boxes() integration for the custom acf_after_title location. Determine how Gutenberg handles the title and metabox areas, then define a supported approach that renders this location and keeps affected field groups visible in Gutenberg.