I want to use cloudflare public dns 1.1.1.1 and 1.0.0.1 in my VPS /etc/resolv.conf right now I use google . Do you advise me to do so ? Is it possible for a VPS?
Yes, it is possible. Be aware that resolv.conf is generated by some programs, so manual change of that file may be overridden in future.
No it is not overwritten at least for the last 10 years that I use variety of linux VPS . I am talking about virtual private servers