Here is the full list of all 15 Arma Reforger achievements.
Flushed a toilet in-game.
Destroyed 25 enemy vehicles.
Neutralized 100 enemy players in any official game mode.
Achieved the rank of major in a single Conflict play session.
Delivered 5000 supplies to friendly bases in a single Conflict play session.
Finished the Combat Ops scenario with every available task completed.
Delivered the enemy intel to the extraction point in the Combat Ops scenario.
Finished the tutorial with every available task completed.
Killed 10 times by other players in any official game mode.
Placed 20 mines in any official game mode, on any official server.
Used a medical item to assist other players 50 times in any official game mode.
Neutralized 500 enemy players in any official game mode.
Used a medical item to assist other players 250 times in any official game mode.
Interacted with a piano in any game mode.
Interacted with a pipe organ in any game mode.