The bug

As of 24w45a, the item_model component now points to resources in assets/minecraft/items, rather than assets/minecraft/models/item. This means that certain item models can no longer be selected like they can in previous snapshots.

How to reproduce

/give @s stone[minecraft:item_model="minecraft:spyglass_in_hand"]

Expected results

A stone item that uses the handheld spyglass model, since spyglass_in_hand is a valid item model.

Actual results

No model.

How to fix

The item_model component needs to be renamed to something more intuitive to indicate more clearly that it doesn't control the item model, but rather one of the item display definitions from that part of the resources.