Here is the location of the hidden Battle Star in the Fortnite Week 3 Utopia loading screen.
The Utopia Challenges for this season have replaced the Discovery Challenges in Season 8, but have been changed slightly. Last season the hidden object would alternate between a Battle Star and a Banner, but this season, you can only find a hidden Battle Star every other week. Fortbytes were introduced this season and some of the Forbyte challenges do involved the loading screens, so this may be the reason Epic have not hidden any Banners this season.
The loading screens have been leaked in the v9.10 update and so we already know the location of the Battle Star. Here is the loading screen for the Utopia Week 3 Challenges:
It can be hard to find the Battle Star in the loading screen, so we have highlighted the location in the image below. The clue for the location of the Battle Star is that it will be on top of an upside truck, which is on top of an ice cream truck, which is on top of an RV which is finally on top of another truck!
The location of the Battle Star is of course at Junk Junction, and we have highlighted the exact location here.
The pile of vehicles you are looking for will be right outside of Junk Junction and we have shown what it looks like below. Remember the Battle Star will only show up once you have unlocked the loading screen.