In the patch note you mentioned that [Amethyst] Clusters can be Silk Touched at any stage.
It works with the latest stage but not with the others.
Amethyst Clusters not working with Silk Touch Enchant
Amethyst Buds are not obtainable with silk touch.
Budding amethyst and amethyst clusters cannot be collected using Silk Touch
Unable to obtain small amethysts on survival