To find Fortbyte number 61 of the decryption challenge, head to the Viking Village and its frozen waterfall, the one on the first floor of the mountain. Don't forget to equip yourself with the "Sunbird" spray which is unlocked at step 26 of the season 9 battle pass (free version), you will need to use it near the Fortbyte to be able to pick it up.
Written by Antonin "Sheybz" Falomir. Translated from French by Millenium.us.org.