Banner Location Guide (Season 8 / Week 4)
To actually get the Banner to appear though, you first need to complete four full sets of any of the weekly challenges (weeks 1-10).
Once any four sets of them have been completed, this secret Banner can be collected and the challenge "Find the Secret Banner in Loading Screen #4" will appear in the Discovery Challenges. It will reward you with one full battle pass tier.
Completing 55 weekly challenges will unlock the secret Discovery skin.