create user, and then database for that user.

sudo -u postgres psql
postgres=# create database mydb;
postgres=# create user myuser with encrypted password 'mypass';
postgres=# grant all privileges on database mydb to myuser;

https://stackoverflow.com/a/75876944/1173856

to enable logins from external systems:

find / -name "postgresql.conf"

find in there listen_addresses = 'localhost', change to listen_addresses = '*'

pga_hba.conf is probably right next to it. add these:

host    all             all              0.0.0.0/0                       md5
host    all             all              ::/0                            md5