Is it possible to bind a domain and a subdomain to different servers?

Question

Domain Name System

I registered a domain name on reg.ru and took hosting from them. I created a subdomain where I am going to install cms and save hosting here, and link the main domain to github pages.
I tried to replace the A records of the main domain with IP github, but after a while they are replaced back with IP reg.ru
Is it possible to do something similar in my case or do I need a separate www-domain, not a subdomain?

Basically, we need your help.

Answer 1

Question resolved. reg.ru technical support turned out to be more competent than their consultants on the hotline.
The main www-domain was created for me as a subdomain with its own folder and a link to this folder, where I installed Wordpress and added two text entries.
I stayed on their free servers ns1.reg.ru/ns2.reg.ru and entered the appropriate entries:

Now the hoster has access to cms and the main domain links to GitHub.
Thanks for the recommendations Victor Taran and Yakov Svetsky

Answer 2

Contact the support service of the place where you edit the DNS zone
A records of different domains are independent of each other

Answer 3

When a client pays for hosting and changes the A record of the domain - most likely they have error protection. If you change the subdomain IP, everything should work. This is a standard scheme, a lot of different things can be hung on a domain through subdomains. If suddenly, which is unlikely, it doesn’t work on reg ru, you can leave hosting there, and delegate DNS management somewhere else, to the same mail ru for business, or he.net