Because Oppo devices often have specific partition setups (A/B partitions), the safest way is to boot TWRP first, then flash it internally if the installation is successful.
fastboot boot twrp_CPH1931_3.4.0_unofficial.img oppo a5 2020 twrp
Once inside TWRP, you will notice:
Developing a post for the Oppo A5 2020 Go to product viewer dialog for this item. Because Oppo devices often have specific partition setups
: Install Minimal ADB and Fastboot on your computer. Phase 2: Unlocking the Bootloader oppo a5 2020 twrp