I did something pretty similar, just with a little bit more readable forEach:

const arr = new Array(n).fill(0);
let result = 0;

queries.forEach(([a, b, k]) => {
    arr[a - 1] += k;
    if (b < arr.length) {
        arr[b] -= k;
    }
});

arr.reduce((a, b) => {
    const acc = a + b;
    result = Math.max(result, acc);
    return acc;
}, 0);

return result;