Here is the full list of all 7 Midvinter achievements. It takes around 0-1 hour to unlock all of the achievements on Windows.
Help the humans in as many ways as you can.
You really do love cats, do you not?
You left the farm in good condition.
You persuaded the Skogsrå to stop the troll.
You stopped the troll together with the Skogsrå.
You eat porridge two days in a row.
You stopped the troll on your own.