Fetch more than 100 messages

What you can do is use an async/await function and a loop to make sequntial requests

async function lots_of_messages_getter(channel, limit = 500) {
    const sum_messages = [];
    let last_id;

    while (true) {
        const options = { limit: 100 };
        if (last_id) {
            options.before = last_id;
        }

        const messages = await channel.fetchMessages(options);
        sum_messages.push(...messages.array());
        last_id = messages.last().id;

        if (messages.size != 100 || sum_messages >= limit) {
            break;
        }
    }

    return sum_messages;
}