Complete greedy algorithm https://en.wikipedia.org/wiki/Greedy_number_partitioning#Exact_algorithm

custom-groups.js

function split(array, groups = 2) {
	array = array.sort((a, b) => b - a);

	const parts = Array.from({length: groups}, () => []);
	const partLengths = Array.from({length: groups}, () => 0);

	for (const item of array) {
		const partIndex = partLengths.indexOf(Math.min(...partLengths));
		parts[partIndex].push(item);
		partLengths[partIndex] += item;
	}

	return parts;
}

index.js

function split(array) {
    array = array.sort((a, b) => b - a);

    const a = [];
    let aSum = 0;
    const b = [];
    let bSum = 0;

    for (const item of array) {
        if (aSum < bSum) {
            a.push(item);
            aSum += item;
        } else {
            b.push(item);
            bSum += item;
        }
    }

    return [a, b];
}