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