Visibility is naturally reduced because of nightly darkness and seasonal darkness. Summer months have more visibility because the UnReal World is set in the far north, where people in real life experience more daylight hours until reaching maximum daylight on the summer solstice on the 21st of June or thereabouts. Then visibility is gradually reduced until maximum darkness on the winter solstice on the 21st of December. It's a feature, not a bug.
The calendar of the current version divides seasons by fantasy month names, and the seasons are divided by the natural equinox and solstice events. One of the post-v3.16 updates introduced actual night time visual effects, but this is easily disabled on the ini configuration file.
Zooming: you use your mouse's scroll wheel or ctrl plus -/+