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