Here is the full list of all 19 Doki Doki Literature Club Plus! achievements. It takes around 6-8 hours to unlock all of the achievements on Windows.
Review Paula's project plan.
Achieve 100% data collection.
Finish all of the Side Stories.
Spend 20 minutes listening to music on the desktop.
Find Dan's special note.
Listen to a lot of what Monika has to say.
Write a perfect poem for Yuri.
Write a perfect poem for Natsuki.
Draw boxes on the desktop.
Write a perfect poem for Sayori.
Delete Monika twice while getting deleted zero times.
Love, Monika
Ruin the game.
Write a perfect poem for Monika.
Write a poem in 20 seconds or less.
Choose not to quit DDLC.
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Start a New Game.
Spend enough time during the poem minigame for the music to loop.