The cache-control header value you have shown is not coming from this plugin but coming from SG Optimizer plugin. If you would like to use this plugin for page caching and cloudflare caching, then you have to first put your domain in your cloudflare account, change the name servers to point to cloudflare and make sure that the domain is managed by your own cloudflare account and not via siteground’s cloudflare account. As you can see your domain is now pointing to sitegorund nameserver: https://i.imgur.com/ESA8NWv.jpeg
Also in the SG optimizer plugin you need to disable all page caching operation and also disable the cloudflare integration in the SG optimizer. Then inside this plugin connect it with your Cloudflare account’s email and API details.
Then this plugin will actually be using your cloudlfare account. Currently your site is using Cloudflare via Siteground’s cloudflare account via their system and not actually connected to your own cloudflare account.
Similar/Helpful thread: https://www.ads-software.com/support/topic/siteground-feature-clone/
