Hi @Mustafa_Ali, the problem would be similar to what has happened here:
In short, .replaceAll() is supported by your browser (which is why it would be working in the preview), but not the Node.js version your n8n instance is using. Instead of using .replaceAll(), you could simply use .replace() and should get the desired result.
To replace multiple occurrences of <br /> using .replace() instead of .replaceAll() you could use .replace(/<br \/>/g, "").