I guess blockquote is now using nested blocks. But I can't add cite in Quote block now.
cite.
cc: @jasmussen
Thanks for reporting this. It seems to have been a regression from https://github.com/WordPress/gutenberg/pull/6054
It actually _is_ possible to add a citation, you have to select the quote _parent block_ in order to do so:

As more blocks get converted to using child blocks, we should find a better way than the hover breadcrumbs to select child blocks.
Also related, #6459
Ahaa, that's hidden well:) _Write citation_ placeholder could just be there all the time.
Closing per reverting of #6054