WordPress filter post content with PHP before editing it in Gutenberg

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.