Some discussion of Gutenberg and post-kinds support here: https://github.com/dshanske/indieweb-post-kinds/issues/190
I don’t seem to be able to select the post kind. It defaults to ‘note’, so if I’m posting a note, that should work fine. But for other types I think I’ll need to stick to the Classic editor for now.
Trying out the Gutenberg editor – fingers crossed everything still works reasonably well for an indieweb note post.