Well, it's not a complete openness to deliberations, obviously. New Zealand has a somewhat more open system, where background records are released very soon after decisions are made.
The 20-year time limit is excessive by far. Cabinet records can only be withheld for 10 years in Nova Scotia. The latest Commonwealth FOI law in the world, that of Ghana in 2019, has a fine harms test for cabinet records, which can only be withheld if they would “undermine the deliberative process”. Well, not all cabinet records released would undermine the deliberative process. It needs to be more precise and nuanced.