Photo libraries only offer at most 4K resolution images when viewing from mobile devices. Due to this images appear soft and have compression artifacts. The issue can be exacerbated if the image is high resolution and in portrait because the long edge will be scaled to the low horizontal resolution of 4k(2160). An image that is originally 3840×5760 will get resized to 1440x2160, a 62% reduction. This limitation is mostly OK for TV viewing, but since viewing distance is much shorter and it’s so easy to zoom on a phone the limitation is much more apparent. The quality of the resized image is also low, but in my testing most of the lack of sharpness was due to size. Images also sync at this lower quality. The only way to view a higher quality image is to use the download feature and store it outside of the Plex app.
To me, high resolution images are essential because I would like to use this as my main photo application. I view photos mostly on my phone, not my TV. If full resolution isn’t possible, at least make higher resolutions and better quality compression possible.