Assuming your bootloader is now unlocked:
Since unlocking the bootloader and flashing TWRP will format your data partition, back up your photos, contacts, and documents to Google Drive or an external SD card.
The OPPO A5 2020 is a solid mid-range device, but like many OPPO phones, it comes with a locked bootloader and no official TWRP support. Thanks to developers on XDA and Telegram, unofficial TWRP builds exist for this device. However, installing TWRP requires unlocking the bootloader, which is not officially supported by OPPO for this model.
⚠️ Warning: This process will wipe all your data, void your warranty, and may brick your device if not followed correctly. Proceed at your own risk.