Just wanted to post this because it might help someone. It is mostly only useful to people who have been greenlit on Steam, but can also be of interest to those who are considering whether to apply to Steam or not. This tutorial shows how easy it is to add Steam achievements to your Unreal game.
Adding Steam Online Subsystem
Go to https://partner.steamgames.com/ and download Steamworks SDK
Follow the official tutorial at Online Subsystem Steam | Unreal Engine Documentation
Close and re-open your project
Steam doesn’t work from within editor, launch a standalone game (Play -> Standalone) to test. If everything works fine, you will see a Steam icon in the lower right corner and Steam overlay will appear if you press Shift-Tab.
You will need a game that has been greenlit on Steam to fully use Steam Achievements, but you can test some of the functionality right away by using the Space War demo app id.
(only if you have been greenlit) Go to your Game Admin page and set up the achievements.
in your game’s DefaultEngine.ini under [OnlineSubsystemSteam] add your achievements like this:
In your blueprints, create these two nodes:
In the “Write Achievement Progress” node replace ACH_TRAVEL_FAR_ACCUM with the name of your achievement and replace 100 with the amount of progress you wish to grant the player.
That’s all It should unlock the achievement at the start of the game.