Postgres 14

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CREATE TABLE "Media" ("Details" jsonb)
INSERT INTO "Media" VALUES('{"Type": "VIP", "Quantity": 1}')
1 rows affected

Update "Media" set "Details" = "Details"
|| ('{"Subscription": "' || ("Details"->>'Type')::Text || '"}')::jsonb
||'{"Type":2}'::jsonb
            
1 rows affected

SELECT * FROM "Media"

Details

{"Type": 2, "Quantity": 1, "Subscription": "VIP"}