Unable to connect to postgres using docker compose - postgresql

Question

I have a very simple docker-compose.yml file which currently is only to set up a posgresql database, but I can't connect to it once it is running. Instead I get this error:
2022-10-10 11:19:41.820 UTC [43] FATAL: lock file "postmaster.pid" already exists
2022-10-10 11:19:41.820 UTC [43] HINT: Is another postmaster (PID 1) running in data directory "/var/lib/postgresql/data"?
The docker-compose.yml is:
version: "3.9"
services:
db:
image: "postgres"
restart: always
environment:
- POSTGRES_USER=postgres
- POSTGRES_PASSWORD=postgres
ports:
- '5432:5432'
volumes:
- /pgdata:/var/lib/postgresql/data
When I try to connect to the running container I use:
docker exec -it -u postgres 31f122d6a413 postgres
The logs from the container are:
Recreating test-docker-proj ...
WARNING: Service "db" is using volume "/var/lib/postgresql/data" from the previous container. Host mapping "/pgdata" has no effect.
Recreating test-docker-proj ... done
Attaching to test-docker-proj
db_1 |
db_1 | PostgreSQL Database directory appears to contain a database; Skipping initialization
db_1 |
db_1 | 2022-10-10 11:05:02.349 UTC [1] LOG: starting PostgreSQL 14.5 on aarch64-unknown-linux-musl, compiled by gcc (Alpine 11.2.1_git20220219) 11.2.1 20220219, 64-bit
db_1 | 2022-10-10 11:05:02.349 UTC [1] LOG: listening on IPv4 address "0.0.0.0", port 5432
db_1 | 2022-10-10 11:05:02.349 UTC [1] LOG: listening on IPv6 address "::", port 5432
db_1 | 2022-10-10 11:05:02.352 UTC [1] LOG: listening on Unix socket "/var/run/postgresql/.s.PGSQL.5432"
db_1 | 2022-10-10 11:05:02.356 UTC [22] LOG: database system was shut down at 2022-10-10 10:47:01 UTC
db_1 | 2022-10-10 11:05:02.361 UTC [1] LOG: database system is ready to accept connections
It seems that postgres/docker is persisting user login details from previous containers or something? I am at a bit of a loss anyway, so any guidance would be appreciated.
I am using:
Mac Monterey M1
docker-compose version 1.29.2
Probably worth adding that I can connect to the container using /bin/sh rather than postgres