Great question and I can definitely understand how messaging like you showed in your screenshots is really important for your customers.
Our standard plans (Basic, Shopify, Professional) do not allow the customization of the checkout experience to be able to add those kinds of pop up messages or embedded banners. This is to protect the integrity of the checkout itself.
Generally we recommend for merchants to look at customizing the cart page to add those kinds of messages. You can also look at a "Terms and Conditions" app that adds a mandatory/optional checkbox on the cart that needs to be marked off before the customer can move to the checkout stage. This is helpful to ensure that customers are taking the time to read any important terms or information they need to know before finishing their order. This can also be manually coded into the cart if you or someone on your team has experience making coding edits.
Shay | Social Care @ Shopify - Was my reply helpful? Click Like to let me know! - Was your question answered? Mark it as an Accepted Solution - To learn more visit the Shopify Help Center or the Shopify Blog