I found another link that describes how to enable track IP visitor on apache2 server with some repositories from Cloudflare, So is that possible if I configure it on my backend server?
While true, it’s mainly so that customers who previously used a different CDN would not have to change anything on the backend, as that header is used by a major CDN. It’s the same as CF-Connecting-IP, which is in every request.
I tend not to use XFF in your scenario as it is not always a single client IP, and can be a chain of IPs you need to process.
The link by @matteo is generally the quickest and most reliable to get the correct outcome.