CloudFlare+Github Pages+own domain, DNS setup on the CloudFlare side. How to correctly register DNS-s?

Question

Domain Name System

Essence of a question:
There is a domain. There are Github Pages. Made a domain binding to Github Pages. I did it in the following way: I created a CNAME file in the repository, added the "[mydomain.ru]" entry there, respectively, added two A lines with githab IP addresses and one CNAME entry where I indicated [myusername].[github].io. The site on github pages has earned everything ok on my domain. Further, accordingly, there was a need to add SSL, googled CloudFlare, added a website. Created certificates. Then I added DNSs provided by CloudFlare to the registrar's personal account. During the day, everything was delegated. As a result, the site does not open says "I can't access the site" (What should I do where to run? I don't understand where to dig, I think the problem is in CNAME, I guess I wrote it wrong somewhere, xs

Answer 1

Start simple.
Ask nslookup - make sure the ip is correct.
If the ip is correct, then the web server or frontend is configured incorrectly.
If incorrect, then see which ns server is responsible for your zone (nslookup -q=ns <domain>), as far as I understand now your records on cloudflare. Check the correctness of the entries.
If the records are kept by the correct dns, but they lead to the wrong place, correct them.
Remember that A records must also be, in addition to CNAME.