“Checkout Thank You” is an element created for the Checkout thank you page and can be used only on the checkout page. If you are using it on another page it will not display and not be of any help. The “Checkout Thank you” element will show up only if you have WooCommerce installed as a plugin.
The Thank you page can be overwritten from the theme builder by creating a new template and selecting “the thank you page” option
You can then edit the theme builder component
And finally, add your checkout thank you element to the page and customize it as you want.