Previous articles in this site have stated that it's not true 2x4k. The screens are, but it's actually upscaled in order to make it possible to be driven by current hardware (please, fact check on my statement?).
I don't think there will be a way to "shut down" the scaler once gpus are good enough for real 2x4k, though.
Pimax 8K does not run anything at 8K. It has double 4K LCD panels that run upscaled WQHD (1440p) signal at roughly 80 Hz, while Pimax 5K has double WQHD OLED panels running native resolution signal at 90 Hz. However since Pimax as company is terrible at giving accurate and timely technical information, even those numbers might not be 100% correct. It's unclear why Pimax claims 5K runs better than 8K, since both have same input resolution with 5K having even higher refresh rate. Possibly the panel makes it appear to run smoother even on low refresh rate? They haven't explained it and M1 prototype testers are still under NDA. We will know more in the future.