franklin@slat.org writes:

Import list data (from 2.1): https://docs.mailman3.org/projects/mailman/en/release-3.0/src/mailman/comman...

You should have a "mailman" command, with "mailman import21 -h" giving brief usage instructions. I gather this succeeded in importing your list configuration(s).

How do I import an archive into a new mailing list: https://wiki.list.org/DOC/How%20do%20I%20import%20an%20archive%20into%20a%20... The second is very old, written in 2007, and now I even can't find bin/arch commands.

Mailman 3's initial public release was at the end of April 2015. Any information dated before that is likely dangerously wrong for recent Mailman 3.

And when I tried django-admin hyperkitty_import it even told me "Unknown command: 'hyperkitty_import'".

django-admin is somewhat finicky because it is intended to serve multiple Django instances, applications, and projects on the same host. It depends on where you start it and which settings.py you feed it. On Debian, you should install the "mailman3-web" package, which provides the "mailman-web" command which integrates django-admin functions from HyperKitty, Postorius, and django-mailman3.

"mailman-web help hyperkitty_import" should tell you how to import your archives.

Steve