I have just upgraded the lists.mailman3.org Mailman 3 installation to the heads of the GitLab mailman* branches. A major change is the switch from Persona to Django Allauth. This requires some configuration which isn't yet complete. Hopefully it will all be working very soon.
In the mean time if you want to log in to Hyperkitty/Postorius you should be able to log in with your email address. The first time you do this, Mailman probably won't even know your password so you'll have to request a reset. Once you have reset your password, you should be able to log in.
I hope to have several social auth choices working very soon.
-- Mark Sapiro <mark@msapiro.net> The highway is for gamblers, San Francisco Bay Area, California better use your sense - B. Dylan