The last day of Christmas
The last day of Christmas is called Þrettándinn (Threttandinn) - which literally translates to "the thirteenth", and is the equivalent to the twelfth night of Christmas, but because Icelanders celebrate their Christmas on the 24th, it's called the Thirteenth, instead of the Twelfth night.
It is the day where all the Yule lads, their parents Grýla & Leppalúði, along with the Christmas cat, trolls, and elves, head back to the mountains and bid their farewells until next Christmas. The Christmas lights are also turned off, the Christmas tree is taken down and the Christmas decorations are put in storage until next Christmas.
Under normal circumstances big bonfires are held, where people gather to light the last fireworks from the New Year and sing New Year's songs and elves songs together, but because of the pandemic it has all been canceled this year.