I was checking options in settings and I applied default theme. Now I can't take it off. I checked on internet how to fix it, but apparently you need oppo theme store
Theme Store - realme Community
Oppo ColorOS releases eight free global themes - Gizchina.com
ColorOS 13 Theme for Realme and Oppo devices - YouTube
Télécharger Theme Store 9.1 APK pour Android Gratuit