The Heroic Games Launcher currently supports GOG, Epic Games and manual side-loading but Amazon Games support is also being worked on.
We're also really close to the next major release of Heroic, which was due out towards the end of last month but got held up by some last minute bugs. So expect it quite soon!
As for Amazon Games support going by the in-progress Pull Request on GitHub it will support displaying your games, installing, updating and running them all through Heroic thanks to the Nile project. Which will be quite nice, since you can pretty regularly get some great free stuff via Prime Gaming.
The developer working on it mentioned it has been tested working across Linux, macOS and Windows and it will work on Steam Deck too via Flatpak.
This is the great power of open source, people come together to build something to make grabbing games from other platforms really easy. Nice to see Heroic continue to get even better.
Find out more about Heroic on the official site.