URL is not intended to go into ALLOWED_HOSTS. Domain names or IP addresses are intended. https://netboxlabs.com/docs/netbox/configuration/required-parameters/#allowed_hosts
Environment documentation only identifies netbox.env, when service environment variables for Postgres and Redis containers are in separate files. Also, production configuration recommends changing DB_PASSWORD var without mentioning POSTGRES_PASSWORD var. If these aren't both changed, the container will not be able to auth to the postgres container.