You usually cannot create PTR records for IP addresses that you do not own. As neither you nor Cloudflare owns those IP addresses, you cannot create PTR records for them in the Cloudflare dashboard. In the screenshot above you have essentially created a PTR record on 126.96.36.199.in-addr.arpa.example.com.
It is possible your hosting provider (Contabo) supports creating PTR records for the IP addresses assigned to your virtual machines. You would have to consult Contabo’s documentation for more information on how to do this.