Just wanted to make sure I understood correctly metaboxes with Gutenberg, and have an additional question.
With WP classic editor all post metadata has a relation with the actual post Object. With Gutenberg, even though the metadata is stored in the DB with the same relation to the post id, from your example it looks like in the UI the metadata is related to a specific block and not entirely to the post Object as the way that the metabox only displays when the block is selected and therefor the metabox wouldn’t event be available if the block is never added.
Wondering if there is a way to have metabboxes render permanently in the Gutenberg editor as you would depend on the user adding a certain block to have the metabox available, which is the way to go in cases where you need mandatory data saved as postmeta?
Would you need to add a “Metabox Block” with all the required fields by default when you create a new post (assuming this is possible)?