If you still want to experiment with a custom ROM (unofficial), here are the general steps — but note this requires , custom recovery (TWRP) , and will void your warranty (if any remains), break OTA updates, and may cause instability.
Once known as the "Selfie Expert," the OPPO F1s was a favorite for its front-facing camera. However, its journey with official software updates ended years ago. oppo f1s android 11 update download