UnlockTool does not directly flash .ozip (encrypted Oppo files). You need a decrypted scatter file.
This post is for educational purposes. Always have permission from the device owner before flashing. flash oppo a53 via unlocktool
Flashing will wipe your data. This guide is for the Oppo A53 (CPH2121) . Do not use it for the A53s (different chipset). Proceed at your own risk. UnlockTool does not directly flash