May I ask have you tried using a different Web browser, or tried clearing your Web browser cache?
How about using a Private window (Incognito mode) or a VPN connection if possible?
Is it the same behaviour on your mobile phone (4G LTE, mobile data, cellular)?
Before moving to Cloudflare, was your Website working over HTTPS connection?
You could determine if this behaviour continues even by using a “Pause” option at Cloudflare as follows from below?
Use the “Pause Cloudflare on Site” option from the Overview tab for your domain at dash.cloudflare.com .
The link is in the lower right corner of that page.
Give it five minutes to take effect, then make sure site is working as expected with HTTPS without any error
Check with your hosting provider / cPanel AutoSSL / Let’s Encrypt / ACME / Certbot and manually click to renew it
Only then, when your website responds over HTTPS, you should un-pause Cloudflare and double-check your SSL/TLS setting to make sure it’s Full (Strict).
Make sure Always Use HTTPS and Automatic HTTPS Rewrites features are enabled at Cloudflare.
Here is a way to re-check if you correctly setup the SSL for your domain with Cloudflare:
In case you do not have an SSL certificate, you can use Cloudflare SSL, if so, kindly make sure you follow the instructions as follows on the below article to setup an SSL certificate using Cloudflare Origin CA Certificate:
Furthermore, do not skip below step and kindly re-check if Cloudflare is allowed to connect to your origin host (firewall, etc.) to as follows in the below article:
Nevertheless, Cloudflare IP addresses list can be found here:
Please, take a note to have HTTPS on WordPress too. Could you also write back if your WordPress is configured with “home_url” and “site_url” in the “Options” and working fine over a HTTPS in a different Web browser just for testing purposes.