To enable secure HTTPS connections through Cloudflare, your website must have a valid SSL cert installed.
It is completely acceptable to keep Cloudflare proxy (orange cloud) enabled. However, if your website does not have SSL, the HTTPS connection between Cloudflare and your server will not be secure.
VPSSIM supports installing free Cloudflare Origin SSL certificates — this is the recommended option when using Cloudflare as a proxy (to hide your real VPS IP).
Once the SSL is properly installed, you can use Cloudflare proxy and HTTPS together safely, efficiently, and securely.