Gutenberg is an excellent editor and would have the capability of simplifying one of some my websites if it could support the inclusion of custom Drupal blocks.
Add a drupal custom block to Gutenberg → says "if you implement a custom block in your module you can enable this block for being used in Gutenberg in the content type Gutenberg configuration". This is certainly not the case on my websites. I cannot see anything that I have created in /src/plugins/block.
This is supported by this post on Drupal Answers is-there-a-way-to-enable-the-gutenberg-editor-so-i-can-use-it-with-custom-blocks, which says "Currently, it's not possible".
I would like to register this feature request for future development since the lack means that I cannot use Gutenberg to its fullest capability.
Postponed: needs info
2.4
Code
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It's likely this issue predates Contrib.social: some issue and comment data are missing.
I think maybe what this person is asking, or at least what I am, is being able to create inline custom blocks like you can within Layout Builder but within the Gutenberg block editor. It seems like you can only add reusable custom blocks right now (those that exist within the Custom Block Library), not one-off custom blocks. I could be wrong though!