Well, I'm now on my third installation of mailman3.  I ran into a problem I had forgotten about but once I figured it out, *then* I remembered running into it last time.

Configuration:  Ubuntu 24.04 ib a vos,

It's this.  I'm a mysql person, not a postgres person, but I installed postgres for this installation just so I could follow the instructions directly. Whenever I tried to start the mailman service, I got the error that mailman didn't have permission to do whatever needed to be done.  The error was:

psycopg2.errors.InsufficientPrivilege: permission denied for schema public

After a little searching, I found out that mailman needs to be made the OWNER of the database, not just granted all privileges.  After adding the commands:

ALTER DATABASE mailman  OWNER TO mailman; ALTER DATABASE mailmanweb  OWNER TO mailman;

I suggest adding those two lines to the instructions for "Setup Database" at https://docs.mailman3.org/en/latest/install/virtualenv.html

billo