Did you make the change? What “more serious error” did you see when you did? It’s entirely possible that mysqli is still the right setting, but it’s not the only problem with your site.
Your website is returning a Cloudflare “Invalid SSL certificate” error for me now. That’s a completely unrelated to any database settings, but rather a problem with the SSL settings of your account.
We recommend using Cloudflare with a self signed SSL certificate on your hosting account, with Cloudflare in “Full” SSL mode.