Oppo A83 Custom Rom Online

It booted into TWRP. The touch screen was unresponsive for a terrifying three seconds, then it jumped to life. He swiped to allow modifications. He backed up his stock ROM (a safety net he was glad to have, though he hoped never to use it).

For OPPO A83 with MediaTek:

fastboot flash recovery twrp-a83.img

Appendix: Minimal checklist before flashing oppo a83 custom rom

fastboot boot twrp-xxx.img

Installing custom ROMs and unlocking the bootloader may void your device's warranty. Additionally, there's a risk of bricking your device if not done correctly. Proceed at your own risk. It booted into TWRP