Docker setup on Ubuntu 20.04

[Str1atum]

I try installing miniflux on a Raspberry Pi 4b with Ubuntu 20.04 LTS and fail.
I use the basic docker script from Github and it all starts with the following error message:

FATAL:  password authentication failed for user "miniflux"
DETAIL:  Connection matched pg_hba.conf line 100: "host all all all scram-sha-256"

I did not change any of the default passwords but I can change to the "postgres" user and log into psql correctly. I even manually added a user "miniflux" with a database "miniflux" but that didn't work either.