There will be Gutenberg (block editor) user documentation in the new HelpHub that's currently being migrated to .org by the docs team right now.

The docs folks are working in tandem with Chris Van Patten and the Gutenberg docs team to make sure block editor docs are part of the HelpHub migration and launch. Lots of moving pieces but the teams are pushing hard to get all of that up and launched in time for the 5.0 release.