I have a problem with using automatic and semi-automatic modes. For example, I have "fairly optimal" light, in "A" mode I set the desired aperture value, let it be 2.8 and ISO 200, when I switch to live view mode on the LCD screen, everything is ok, depending on the conditions I get low shutter speed (down to 1/800s). After switching to the viewfinder, the time increases immediately to huge values, even up to 30 seconds. I can change ISO and aperture both ways, but the time does not change either at all or the change is minimal, it "works" the same in any automatic mode, I tried it for both lenses, for different lighting conditions. The LCD screen displays a warning that "the subject is too dark", the time does not change when I put my eye to the viewfinder. Pictures come out all white (no surprise), in addition, in the AUTO mode the flash always fires.
I restored the factory settings, reset all user settings, formatted the memory card, downloaded the current firmware from the Nikon official website, and reinstalled. Nothing has changed:
LCD preview: ISO 2000 and 2.8 aperture, the shutter speed has been set to 1 / 500s, the photo is ok.
View through the viewfinder: ISO 2000 and aperture 2.8, the shutter speed changed to 30s, while i changed the exposure compensation to -5.0, the time dropped to 1 / 20s, the photo came overexposed.
In manual mode (and automatic when previewing on LCD) everything works rather well, I took several hundred photos and I did not notice any problems with sharpness, the changes in parameters are visible, I'm even able to shoot in weak light conditions, so I do not understand if my Nikon is simply faulty, whether I am doing something wrong or do not understand something about its principle of operation.