Oppo generally makes it very difficult to unlock the bootloader, which is required for custom software. Hardware Limits:
A new confirmation screen appeared, one he had never seen before: oppo f1s android 11 update download
If you want to run Android 11 on an Oppo F1s, your only option is to use developed by the community (such as LineageOS or Pixel Experience). Important Considerations for Custom ROMs: Oppo generally makes it very difficult to unlock