Use manual achievements - Lacro59/playnite-successstory-plugin GitHub Wiki

The manual achievements is only for the legit games. It's impossible to add manual achievements for a game without store.

1. With the game menu, you can Add the achievements list.
   The list downloads from Steam if the game exists in the store and there are achievements.

2. If there are achievements, you can Edit the list achievements with the game menu.

3. In the edit view, you can unlock achievements with or without a date.

example: