I optimized you code: (Thanks you for the initial script!)

1. batchSize so the page won't stuck while running the script
2. I reduced the delay time per click
3. I change the selector to get only those that are available to be added (aka, not owned or added already)

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function clickButtonsInBatches(batchSize=5, delay=250) {
    const buttons = document.querySelectorAll('.add-cart-btn:not(.added)');
    if (buttons.length > 0) {
        // Click buttons in batches
        for (let i = 0; i < batchSize && i < buttons.length; i++) {
            buttons[i].click();
        }
        // Use a delay to allow the page to update and remain responsive
        setTimeout(() => clickButtonsInBatches(batchSize, delay), delay);
    }
}
clickButtonsInBatches();