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