Want to ask something

Good morning.
I hire a mail service, with my own domain, but from where I register the domain, it only allows me to alter the DNS servers and not the MX settings, and I must configure the MX, the DNS of my domain are pointing to the DNS servers of whom hire the mail service, what I want to know is that if I configure the MX from cloudflare will the mail work? or should I configure the DNS servers to point to Cloudflare’s DNS?

Absolutely. If you want to use Cloudflare you have to use their nameservers.