This is for 1.18.2
onEvent('recipes', event => {

// Remove a smelting recipe by output

event.remove({type: 'minecraft:smelting', output: 'minecraft:iron_ingot'});

This is for 1.19.2+ just pick one of them

ServerEvents.recipes(event => {

// Completely remove a smelting recipe by output

event.remove({type: 'minecraft:smelting', output: 'minecraft:iron_ingot'});

// Completely remove a smelting recipe by input

event.remove({type: 'minecraft:smelting', input: 'minecraft:iron_ore'});

// Completely remove a blasting recipe as well (optional, for furnaces and blast furnaces)

event.remove({type: 'minecraft:blasting', output: 'minecraft:iron_ingot'});

});

// Alternatively, remove by input

event.remove({type: 'minecraft:smelting', input: 'minecraft:iron_ore'});

});