I have been trying to reproduces a curios from beneficium by making it gives 500%
I used the attributeslib:experience_gained by adding 500% but nothing changed.
I'm on forge 1.20.1 using ApothicAttributes-1.20.1-1.3.7

I'm using KubeJS to make the curios with the attribute, here is the code. I'm launching experience bottle to check if it works but I still get the same amount of experience. Here is my code if you know a bit about kubejs, everything is working, the tooltip is showing but the experience gain is the same. You can copy the code and try it yourself if you want, I'm using KubeJS+PowerfulJS to simulate that.

StartupEvents.registry("item", event => { event.create('talisman').displayName('§eTalisman').maxStackSize(1).rarity("rare").glow(true).tag("curios:charm"). attachCapability(CuriosCapabilityBuilder.CURIOS.itemStack() .canEquip(((item, context) => true)).canUnequip(((item, context) => true)) .modifyAttribute("attributeslib:experience_gained","experience_gained",5.0,"multiply_total"));//attribute showing on tooltip but doesnt work at all event.create('divine_talisman').displayName('§dDivine Talisman').rarity("epic").glow(true).maxStackSize(1).tag("curios:charm").attachCapability(CuriosCapabilityBuilder.CURIOS.itemStack() .canEquip(((item, context) => true)) .canUnequip(((item, context) => true)) .modifyAttribute("attributeslib:experience_gained","experience_gained",15.0,"multiply_total"));//attribute showing on tooltip but doesnt work at all })

Experience Gained only works on xp drops from entities and blocks, it doesn't work on bottles of enchanting.

How are you attempting to verify if it works?