If you’re using your full domain name as example.com and also want www, you should consider adding and using only CNAME setup.
My domain example.com is registered via 3rd-party domain registrar and actively using Cloudflare nameservers.
Nevertheless, when you add your custom domain or sub-domain, you’d get a pop-up message like below:
We were unable to verify our authority for that domain.
On the domain registrar’s website, find the Domain Name System (DNS) settings and enter the following two CNAME values: (name: cftest, destination: ghs.google.com) and (name: zdmvmakeler2, destination: gv-xxxxxxxxxxxxxxx.dv.googlehosted.com).
See Set up a custom domain - Blogger Help for detailed instructions.
In my case, I’ve used CNAME and sub-domain cftest.
Under the Blogger, you’d have to make some changes e.g.:
At Cloudflare DNS records:
Since the CNAME DNS records are proxied and 
, to make it work under the SSL/TLS settings you have to use Flexible SSL.
Or, in my case, since it’s sub-domain I’ve created a Configuration Rule under the Rules tab for my cftest sub-domain to use SSL Flexible:
At the beginning, before your domain or sub-domain is active with unproxied 
CNAME records, you’d experience either 404, or even for Flexible some 301 redirect (but with HTTPS enabled at Blogger), or if you’re having Full or Full (Strict) you’d have SSL handshake error.
Create your first page test and publish it, therefrom create your first blogpost and publish it as well.
I can confirm my setup works fine, done in few minutes ago:
Later, add A www pointed to the 192.0.2.1 and proxied .
Using Redirect Rules under Rules tab, you can redirect www to non-www or sub-domain. Helpful article.
Regarding the SSL issue for Google, you might have some issue getting it at first if you’re using some Custom Rules for WAF since Google Certificates would try to request an SSL for your (sub)domain:
