Check the resolution of the eyepiece; its not even HD.
Yes, it will take a 4K signal, but it displays 1440 x 980.
Just because it can receive a 4K signal, doesn't mean you are looking at a true 4K image; it has been decimated to fit the lower resolution of the screen.
Besides the aspect ratio of the viewfinder 16x9 will require further cropping for your 4:3 images, lowering even more the resolution you will get on your camera.
When HD designers decided to arbitrarily restrict high resolution video to panoramic or wide screen aspect ratios, they did a great disservice to classic aspect ratio images.
At best I suggest you find an 4K OLED monitor that can display over 90% Rec. 2020 color space and build a light tight box around and shoot the screen with a good flat field lens.
And, you'll need to learn a bit of color science to make sure you both calibrate and get accurate colors to the monitor.