Here is the full list of all 15 If Found... achievements. It takes around 3-4 hours to unlock all of the achievements on Windows.
Erase for the length of one Mass.
After finishing the first chapter, go to the last chapter.
Choose the Mayo flag in the character creator.
(That we may live to see this time next year.) Write every diary entry in Opening.
Finish ‘Opening’ chapter.
Choose the transgender pride flag.
Draw for the first time.
Finish ‘The Anomaly’ chapter.
Finish ‘The Back of Beyond’ chapter.
Finish ‘Cassiopeia was over Keel’ chapter.
Play the game in Irish.
Finish ‘Coming and Going’ chapter.
(Do you understand?) Read an Irish annotation.
Find Colum drinking coffee.
Erase for the first time.