Summary:
High level of thorn enchantment no longer causes high damage.
For example, in version 1.20.6, a netherite chestplate enchanted at level 255 can kill mobs such as husks with one hit, but 24w18a this is now broken.

Steps to reproduce:

1. Launch the world on version 1.20.6.
2. Switch into survival mode and equip an item enchanted with thorns by using the command provided below.

   /give @p netherite_chestplate[enchantments={levels:{"minecraft:thorns":255}}] 1

3. Summon an entity that will attack you, for example, a husk.
4. Let it damage you.
5. Launch the world on version 24w18a.
6. Repeat steps 2-4.

Observed result:
On version 1.20.6, the husk dies in one hit, while in version 20w18a it does not.

Expected result:
Husk dies from one hit.

Video:
24w18a_thorns_255.mp4
1.20.6_thorns_255.mp4