DButton no longer supports @action as a string. Please refactor to use an closure action instead

You can find detailed information about modern Ember actions here: Component State and Actions - Components - Ember Guides

But essentially, the message you’re seeing means that you need to change something like

{{d-button action="blah"}}

to something like:

{{d-button action=(action "blah")}}

If you can share a link or snippet of your code, I’m sure we can help out with some more specific instructions