Get all distinct values of array column PostgreSQL

I have a table that has around 400000 records and lets say it looks like this:

UUID   | setting_ids
 1     |  {1,8}
 2     | {4, 69, 7}
 3     |   { }
 4     |   {2}
400000 | {1, 2, 3}

I have to return all distinct setting ids of column setting_ids which is array type. Right now I have a query like this and it takes around 600ms to execute, which is too slow. I have GIN index on settingIDs but I don't know how to use it right for this type of query.

WITH "t_setting" AS (
        SELECT "t"."setting_ids"
        FROM "test" "t"

), "testt" AS (
        SELECT UNNEST("setting_ids") AS "setting_id"
        FROM "t_setting"
FROM "testt"

Thanks for your help!

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