I had black screens before I manually adjusted the fan speed. Now I can go to 100% and nothing happens, but as soon as everything runs automatically I lose the picture and the fans spin up even though the graphics processor stays cool. MSI Afterburner didn't help either.
I don't know how you use MSI Afterburner but it should be the tool you need to adjust the OC and undervolt your GPU. There are some posts on Reddit that I think will help you learn how to use it to undervolt your GPU; they also include the performance and efficiency results. You can copy the settings, and let's see how it improves the GPU efficiency.
Here read this:
RTX 5090 FE undervolt results