The Ice Legion invaded Fortnite during the Ice Storm event, bringing a lot of new things to the game. One of these things are the Golden Ice Brutes that many players aim to find and kill as part of their challenges, but it's easier said than done to find these guys.
There are three types of enemies in The Ice Legion; zombie-like Ice Fiends, long and thin Ice Wraiths, and the bulky Ice Brutes. The latter one is the one you want, and you can easily tell it apart from the other two mobs by it's large and bulky body size.
All the enemies of The Ice Legion spawns from one of the big Ice Crystals that are shattered all around the maps, so you want to seek out these. Now pray to the RNG gods, because any Ice Brute has a small chance to spawn as a Golden Ice Brute instead.
The Golden Ice Brutes drop better loot than the regular Ice Brutes, but they also require more damage taken before they die. Otherwise they behave exactly the same as the Ice Brutes.
You pretty much need a little bit of luck to find the Golden Ice Brutes, but it won't be too difficult to do if you play a lot close to the Ice Crystals that spawn enemies from The Ice Legion. Good luck!