The bug

The recipe file for netherite scraps has "experience": 2.0, however it provides the exact same amount of experience as gold ore, which has "experience": 1.0. In general, values above 1 are treated as 1.

How to reproduce

/xp add @s -100000 points

/setblock ~1 ~ ~ furnace{Items:[{Slot:2b,id:"cake",Count:1b}],RecipesUsed:{"minecraft:netherite_scrap":1000}}

/xp add @s -100000 points

/setblock ~2 ~ ~ furnace{Items:[{Slot:2b,id:"cake",Count:1b}],RecipesUsed:{"minecraft:gold_ingot":1000}}

Take the cake out of each furnace, you will receive exactly the same amount of experience each time (~26 levels), instead of getting twice as much from the netherite.

Code analysis

AbstractFurnaceBlockEntity.createExperience only multiplies the number of items smelted with the experience value if said value is less than 1.0. Removing this check altogether would probably fix the issue. Its existence is evidence that this is intentional, but that contradicts what appears to be the intention for netherite scraps to provide extra experience.