The bug
The filter will not filter out the specified path in the namespaces that are not "minecraft"
The attachment is a datapack to verify this behavior. It contains a pack.mcmeta that filters out recipes from any namespace and a custom namespace with a recipe and an advancement in it.
How to reproduce
Download the datapack attached and install it to a world
Enter the world
Place down a crafting table, go into its GUI and click open the knowledge book
The custom recipe that is supposed to be filtered out is shown❌
Can confirm.
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