I own a Olympus EM5 Mark 2. When reviewing my pics through the viewfinder, during playback, I have noticed that some of the pics show slight pixelation at max magnification (x14). This is not evident when I view the pics magnified on the LCD screen. Image quality is not affected when I process the pics in either Lightroom or Apple Photos. It seems to happen mainly in bright light, and appears on all lenses. Is this anything to be concerned about?
Many camera bodies can enlarge preview images beyond 1:1, which would result in the image becoming pixelated. The manual for your camera doesn't give any clear indication of whether or not this is the case for yours.
Your camera does have an indication of what part of the frame is being displayed; you might check to see if it changes color at some point in the range of zoom settings, which may be an indication that you're at 1:1 or beyond it. (Again, there's nothing in the manual about this.)
It is normal to see pixelization beyong 100% magnification. In the case of the E-M5 Mark II, 14X is way beyond that. It should be at 100% before 7X actually.
Given that the LCD has a lower resolution than the EVF, it takes more zooming in to achieve 1:1 pixel ratio which is why so see magnification before on the EVF.
Very few cameras tell you when 100% magnification is achieved. I recall the Pentax K-3 does when reaching 8.3X and there are some cameras, from Canon if my memory serves, that allow a custom setting to jump directly to 100% magnification. Otherwise, you just have to learn and remember the right zoom level to get a 100% view.