Can confirm.
Can confirm. What a bug LOL
You should use {} inside the list. idk why but MOJANG seems to forget it.
Modified command, use this instead↓↓↓:
/give @s minecraft:iron_sword[attribute_modifiers={modifiers:[{type:'minecraft:generic.scale',uuid:[1,2,3,4],name:'Big!',amount:1.0,operation:'add_multiplied_base'}]}]
Can confirm.
Can confirm in 24w09a. Hope get fixed soon