Here is the full list of all 26 Outcore: Desktop Adventure achievements.
Played every icon mini game on the desktop
Defeated the mastermind through the HATE route
Defeated the mastermind from the first phase without losing any lives, via the HATE route
Defeated Hartstronk after talking with the time-wasting heart
Passed the lake fairy's test
Witnessed a memory that didn't happen. Probably?
Murdered a Lumi
Defeated the mastermind through the DEMON route
Opened the mastermind door before receiving its password
Found the immersion breaking meta menu
Defeated Booty The Bootleg from the first phase without losing any lives
Completed all of the stages in the idle game
Defeated Captain Tutorial from the first phase without losing any lives
Reached the top of the high striker mini-game
Allow Lumi to achieve her dream of becoming a dead web browser
Defeated the mastermind through the LOVE route
Proved a point by taking an unnecessary self imposed challenge of touching some text during a race