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.
Achieve 100% data collection.
Spend 20 minutes listening to music on the desktop.
Find Dan's special note.
Listen to a lot of what Monika has to say.
Draw boxes on the desktop.
Finish all of the Side Stories.
Choose not to quit DDLC.
Delete Monika twice while getting deleted zero times.
Write a perfect poem for Yuri.
Write a perfect poem for Natsuki.
Review Paula's project plan.
Love, Monika
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Ruin the game.
Write a poem in 20 seconds or less.
Write a perfect poem for Monika.
Start a New Game.
Write a perfect poem for Sayori.
Spend enough time during the poem minigame for the music to loop.