collective.html2blocks helps with migrations from old Plone versions -- and other CMS -- to Volto. It converts HTML and Markdown content into Volto blocks.
Install the converter as a library with pip install collective.html2blocks.
It needs only the converter's own dependencies.
To use the html2blocks command, install the cli extra: pip install "collective.html2blocks[cli]".
To run the HTTP service, install the server extra: pip install "collective.html2blocks[server]".
The all extra installs both.
Read the documentation.