It is located in

/var/lib/postgresql/data/pg_hba.conf

To best setting up, just make a volume to local file, copy content from docker pg_hba.conf and edit local. Default pg_hba.conf file can be found in official docs: https://www.postgresql.org/docs/current/auth-pg-hba-conf.html

If you want to change a host, not forgot to apply env in docker:

ENV POSTGRES_HOST_AUTH_METHOD=trust

also find commands find that file, are you sure that use that in correct location? (root: /)

root@test:/# find . -name "pg_hba.conf"

./var/lib/postgresql/data/pg_hba.conf