What’s the Difference Between HTML’s Dialog Element and Popovers?

Popovers likely have more use cases than dialogs. Any time you need a tooltip or to provide more contextual information that has good reason not to be visible by default, a popover is a good choice.

Non modal dialogs are pretty similar to a popup, but are perhaps better suited to situations where there is no other element on the page that is relevant to the messaging. Perhaps something like a “No internet connection detected” message, which could be very important to tell a user, but doesn’t need to 100% stop other activity on the page.

Source: What’s the Difference Between HTML’s Dialog Element and Popovers? – Frontend Masters Boost