How do High density images on sites like wordpress or shopify?

So in the lesson about high-density images, Mosh shows how we need to resize images and provide different image sizes so that they are correctly displayed on different screens, you know…

We want images to look sharp on iPhone x or on a big TV screen.

That was clear to me, but then I thought about Wordpress or Shopify, do you guys know if these “drag and drop” platforms resize images automatically or is it something we should provide?

Thank you.