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