Is that normal that I have this extra space/section on mobile on the thank you page? Just below the order sumarry.
Not sure if Shopify is designed like that or if this is a bug? If yes how to remove it?
If you are using Shopify plus plan then only you can update the CSS on the checkout page. Else you can't add your additional CSS to the checkout page.
Can you please share your store URL? So I can check and compare with others.