I would not expect anything to change. I’m interested in what certificate is presented by your server, which that command should give. (If you get no result, remove the element after /dev/null, you will get more output but it will contain the certificate details, which is the important bit.)
With SSL Full, you can use any certificate you like, even an expired self signed certificate for the wrong hostname. For Full (Strict) the certificate must match the hostname, must be in date, and must be issued by a trusted CA (or be a valid Cloudflare Origin certificate that matches the hostname).
The only IP address that is relevant is the one you have configured for that hostname in Cloudflare.
You might need to open your hosts firewall if you have blocked access except from Cloudflares IP addresses.
For those interested: I tried with a Lest’s encrypt SSL certificate and the Full (Strict) mode worked, the problem is that when I Log in through WordPress admin, the 526 error reappears, for that I created a Page Rule where I set SSL on Full mode.
But I still don’t know why Full (Strict) mode didn’t work with the CloudFlare Origin CA Certificate.