TFA doesn't say -- does anyone know if this applies to 5k and 6k monitors? On my 5k display on a M4 Max, I see the default resolution in system settings is 2560x1440. Which is what I'd expect.

If the theory about framebuffer pre-allocation strategy is to hold any water, I would think that 5k and 6k devices would suffer too, maybe even more. Given that you can attach 2x 5k monitors, the pre-allocation strategy as described would need to account for that.