Until 25w03a it was possible to hide the additional tooltips of Smithing Templates and Disc Fragments using the hide_additional_tooltip component. However, this has no equivalent in 25w04a since those tooltips are not added by any component but the items themselves.

How to reproduce:

(It's difficult to prove that something isn't possible. Below is a reproduction showing that tooltips show up when updating from 25w03a to 25w04a, but this issue is not exclusively a datafixer issue)

1. In 25w03a run the following commands:

   /give @s minecraft:bolt_armor_trim_smithing_template[minecraft:hide_additional_tooltip={}]
   /give @s minecraft:disc_fragment_5[minecraft:hide_additional_tooltip={}]
   

1. Observe that those items don't have any tooltip except their name
2. Update to 25w04a
3. Observe that those items now do have an additional tooltip

Cause:

These items still create their tooltip in the appendHoverText method of the item subclass. Skipping this method was previously the effect of the hide_additional_tooltip component. Other uses were moved to components but these 2 cases still use this method, which can no longer be skipped.