[HELP]Sapphire RX580 2048SP flashed to RX570 and working, but can't get any signal from Catalina.

Hi guys, I have a Sapphire RX580 2048SP flashed to RX570, the gpu is working fine in Windows and on boot, Catalina recognises it too, but I don't get any signal from that gpu, any idea why? Huge thanks!