The preview of images is light. Upon magnifying the image the image preview becomes darker but when minimised it becomse light again.
It is rendering Lightroom unusable.
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When you select a photo, it becomes the active photo. You can select multiple photos, but only one photo at a time is the active photo. Selected photos are indicated in the grid and the Filmstrip by a thin border around the thumbnail and a lighter-gray cell than deselected photos. The lightest colored cell indicates the active photo. See Select photos in the Grid view and the Filmstrip.