From the screenshot above and developer console I see “Mixed content”.
Kindly, check below article for help how to resolve this issue regarding HTTPS and SSL certificate while using Coudflare:
Regarding ERR_SSL_PROTOCOL_ERROR message, kindly see below:
Seems to me you did not have had an SSL certificate installed at your host/origin server before moving to Cloudflare? Moreover, if you have had it, maybe you have wrongly selected/setup the SSL settings at Cloudflare dashboard.
If so, kindly re-check with the suggestions from the below article how to properly setup the SSL with Cloudflare:
Helpful article about SSL settings available at Cloudflare:
To troubleshoot some more issues, check here:
There is also a possible way of having Flexible SSL or HSTS option enabled at Cloudflare dashboard, while the server is working and/or serving content from HTTP and not HTTPS.