To migrate existing data from a previous major version of PostgreSQL run:
brew postgresql-upgrade-database

This formula has created a default database cluster with:
initdb --locale=C -E UTF-8 /opt/homebrew/var/postgres
For more details, read:
https://www.postgresql.org/docs/14/app-initdb.html

To restart postgresql after an upgrade:
brew services restart postgresql
Or, if you don't want/need a background service you can just run:
/opt/homebrew/opt/postgresql/bin/postgres -D /opt/homebrew/var/postgres

show data_directory;
SELECT  pg_current_logfile();

CREATE USER grafana WITH LOGIN NOSUPERUSER INHERIT NOCREATEDB NOCREATEROLE NOREPLICATION;
ALTER ROLE grafana WITH PASSWORD 'XXX';
GRANT grafana TO postgres;
CREATE DATABASE grafana WITH OWNER = grafana ENCODING = 'UTF8' LC_COLLATE = 'en_US.UTF-8' LC_CTYPE = 'en_US.UTF-8' CONNECTION LIMIT = -1;

REVOKE CREATE ON SCHEMA public FROM PUBLIC;
CREATE ROLE grafanareader WITH LOGIN PASSWORD '<PW>';
GRANT CONNECT ON DATABASE <DB> TO grafanareader;
GRANT USAGE ON SCHEMA public TO grafanareader;
GRANT SELECT ON ALL TABLES IN SCHEMA public TO grafanareader;
REVOKE CREATE ON DATABASE <DB> FROM grafanareader;