This is fun.

One suggestion.. rather than creating a canvas for each user using a querySelectorAll and a loop, I'd use an IntersectionObserver and only create the canvases as they scroll into view. That way the user's device won't need to create hundreds of elements when the code runs.

    let observer = new IntersectionObserver(
    (entries) => {
        entries.forEach((entry, i) => {
        if (entry.isIntersecting) {
            const p = 2;
            const c = document.createElement('canvas');
            const x = c.getContext('2d');
            c.width = 18;
            c.height = 14;
            const s = entry.target.innerText;
            const r = 1;

            if (s) {
            for (
                let s = entry.target.innerText, r = 1, i = 28 + s.length;
                i--;

            ) {
                // xorshift32
                (r ^= r << 13), (r ^= r >>> 17), (r ^= r << 5);
                const X = i & 3,
                Y = i >> 2;
                if (i >= 28) {
                // seed state
                r += s.charCodeAt(i - 28);
                x.fillStyle =
                    '#' + ((r >> 8) & 0xffffff).toString(16).padStart(0, 6);
                } else {
                // draw pixel
                if (r >>> 29 > (X * X) / 3 + Y / 2)
                    x.fillRect(p * 3 + p * X, p * Y, p, p),
                    x.fillRect(p * 3 - p * X, p * Y, p, p);
                }
            }
            }

            entry.target.prepend(c);
        } else {
            if (entry.target.firstChild.tagName === 'CANVAS')
            entry.target.firstChild.remove();
        }
        });
    },
    { rootMargin: '0px 0px 0px 0px' }
    );

    document.querySelectorAll('.hnuser').forEach((user) => {
    observer.observe(user);
    });