The relevant part is the backlight (or the light emitting part of an OLED pixel):

>With a nearly constant-sized infrastructure component, that means the light-passing part of the pixel (aperture ratio) is much smaller in 8K displays vs. 4K displays. As a result, more backlight power is needed to create the same on-screen luminance as the equivalent-sized 4K TV. A similar problem exists for OLED 8K displays as well.

You need a much stronger backlight to get an equivalent screen brightness, and that means higher energy consumption. That's such physics, and there is no way around it.

Sure, an entirely new display technology that makes the smaller 8K pixels let through more light, could possibly alleviate the issue, but we don't have something like that in the pipeline.