Error 1014 means that the target of your CNAME is in a different Cloudflare account, so you cannot CNAME to it unless the target using Cloudflare for SaaS.
this is because I want to have a custom domain in accordance with the rules of said wiki, though I can’t accomplish that if Cloudflare somehow believe I have an Error 1014 in some way, unless I miss something beyond my scope
Then it is as I and the error page told you. You cannot CNAME to a target that is proxied in another Cloudflare account if it is not using Cloudflare for SaaS. And meijinversus.miraheze.org is using the Cloudflare proxy.
If they are using Cloudlfare for SaaS, they need to configure for your hostname at their end.
I see…
I will then try to contact the technicians at Miraheze to see how they can let me potentially fix this, since the situation may be on their end after all.