How to filter post content with PHP before it shows up in Gutenberg editor? I've read the following answers but didn't find what I need:
Answer in Filter post before *editing* suggests using the_editor_content filter HOOK which is wrong because what that hook does is to filter the default editor contact.
Answer in Filter post_content before loading in Gutenberg editor is a JS based solution.
I also tried HOOK content_edit_pre but it doesn't seem to work in Gutenberg.
I've searched https://developer.wordpress.com and didn't manage to find anything related.