I understand you're looking for an Android 11 update for the OPPO F1s (released in 2016). However, I need to provide an important clarification:
If you still want to experiment with a custom ROM (unofficial), here are the general steps — but note this requires unlocking the bootloader, custom recovery (TWRP) , and will void your warranty (if any remains), break OTA updates, and may cause instability. oppo f1s android 11 update download
Unfortunately, there is no official Android 11 update for the OPPO F1s. I understand you're looking for an Android 11
At 2:17 AM, alone in his flat, he pressed Download. Go to Settings > Software Update
Conclusion
Most enthusiast developers have stopped creating software for this specific device. OPPO Global Community
Verify Sources: Many "Android 11 for F1s" downloads found on YouTube or random blogs are fake or contain malware.