Some users want Android 8 for newer security patches. However, unofficial ROMs often have outdated security patches too or introduce new vulnerabilities. Unless you are a hobbyist, the risk outweighs the benefit.
You cannot install a full ROM without a custom recovery. oppo f3 android 8 update download full
If you are determined to experience Android 8.0 Oreo on your Oppo F3, your only option is to root your device and install a Custom ROM. Some users want Android 8 for newer security patches
Warning: This process voids your warranty and carries the risk of "bricking" your phone (making it unusable). You cannot install a full ROM without a custom recovery
Note: Custom ROMs may have bugs, such as non-working cameras, Wi-Fi issues, or battery drain.