Shopify – NextJS: "window is not defined" error still triggered even though using useEffect

I’m trying to integrate a JS library in my NextJS app, but when loading the page I always get the following error on the server-side:

ReferenceError: window is not defined

I don’t understand why this occurs, since I’m using this library inside a useEffect hook. Besides that, I’m also reinforcing it by putting a condition on the window object (which shouldn’t be needed).

import { Draggable } from "@shopify/draggable";
import { useEffect, useRef } from "react";

type DraggableItemListProps = {
    children: React.ReactNode
}

export default function DraggableItemList({children}: DraggableItemListProps) {
    const container = useRef<HTMLDivElement>(null);

    useEffect(() => {
        if (!container.current || typeof window === 'undefined') {
            return;
        }

        const draggable = new Draggable(container.current, {
            draggable: '.draggable',
            handle: '.draggable-handle'
        });

        return () => {
            draggable.destroy();
        }
    }, [children])

    return (
        <div ref={container}>{children}</div>
    )
}

If I remove everything inside the useEffect, and I simply use the window object in any way, it works without any issue.
Can somebody please tell me what I’m missing?

Thank you.