Hi @zooce
You need to think about Docker as separate servers, so localhost in a container is the container itself.
Read more here: Cannot connect to localhost PgAdmin 4 server
Would also recommend specifying an application database, so you don't lose all data if you remove the container:
https://www.metabase.com/docs/latest/operations-guide/running-metabase-on-docker.html#using-postgres-as-the-metabase-application-database
If you're unfamiliar with Docker, then use JAR instead:
https://www.metabase.com/learn/getting-started/getting-started/installing.html