The 4th fortnite fortbyte is located ABOVE Loot Lake and there will be rings you have to skydive through to get it. No emotes or any other requirements.
This one is fairly simple, but the rings can be easy to miss as well depending on how quick you are.
If you’re having trouble getting fortbyte 4, then the below video by InTheLittleWood should help.
If you’re looking for other Fortnite Fortbyte Locations, check out our full fortbyte location list.