Query to return column values as comma separated - postgresql

Question

I am using materialized view in my application.

The query is as follows

SELECT
  DISTINCT n.order_id,
  CASE
    WHEN n.customer_billing = TRUE THEN 'AR (Customer Billing)'
    WHEN n.commander = TRUE THEN 'AP (Commander)'
    WHEN n.agent = TRUE THEN 'AP (Agent)'
    ELSE NULL
  END AS finance
FROM
  pt.notes n
 WHERE
 n.order_id = 891090 AND
  (n.customer_billing = TRUE or n.commander = TRUE or n.agent = TRUE)

This produces the following output

Instead of two records, the output of finance column should be comma separated values.

That is the output should be

AP (Agent), AR (Customer Billing)

I know aggregate functions can be used here, but not sure how to use when the query has switch cases and all.

Any idea on how to achieve this?