This is not a fern but a common houseplant called Chinese Evergreen (Aglaonema). There are a range of cultivars bearing different leaf patterns, and they are cousins to the equally-common Peace Lily.

The watering frequency sounds high, though it depends on how much water is being given each time. Too little at a time may be leaving lower roots too dry, which can kill them over time. The leaf appearance here suggests over-watering, however.

Houseplants should be watered thoroughly enough that excess drips freely out of the bottom pot holes, though at a frequency that lets the top inch or more of potting mix ("soil") get fairly dry before they are drenched again. (There are a few exceptions, but for most houseplants, consistently-damp soil creates conditions that deprive roots of oxygen and can cause root death.) Make sure a saucer used underneath the pot doesn't collect that extra water for long, as this will seep back into the soil and over-saturate the roots; empty it right away or drip-dry the pot over a sink first instead.
https://extension.umd.edu/resource/watering-indoor-plants

The foliage symptoms seen here - markedly off-color and somewhat droopy - suggest root loss has already occurred, probably to the degree the plant is unsalvageable. We suggest you unpot the plant over a trash can, bucket, or tub, and look for how many healthy roots can be seen on the outside of the root ball. If the root ball falls apart pretty easily, that suggests that root growth is poor or has been lost to dieback. Healthy roots are firm, not easy to tug apart, and either white or tan (possibly deeper brown if naturally stained by the potting mix). Dead roots easily pull apart, are brown to black, and may smell musty or sour.

Nutrient deficiency can cause leaf yellowing/bronzing, but as often as not, it's not that the soil is depleted so much as the roots are ailing and not able to absorb what the plant needs, no matter how rich the soil is. In those cases, adding fertilizer does not remedy the problem; ironically, it can actually make it worse.

Replacement would be simplest, but if you wish to try rehabbing the plant, repot it and adjust your watering frequency. While lack of fertilizer for the better part of a year may be part of the problem, since nutrients are used-up or rinsed out of the soil over time, in this case, the plant will need to regrow functional roots before it can make use of any fertilizer. Remove and discard all existing soil and clip off any dead roots you find. Use fresh potting mix and repot the plant at the same depth it was growing before. You probably won't need a larger pot; if anything, if roots are lacking, a smaller pot might be better, since they dry out faster than larger pots. You can clean its empty current pot with just soapy water and a scrub brush if you want to reuse it. Damaged or discolored leaves will not heal themselves, so will need clipping off near the base of their stems. New growth may take weeks to appear, since roots will probably need to be replaced before foliage can develop.

The light levels you describe are probably ok, but a window with direct light in a northern or eastern exposure might be preferable; or, you can just move it slightly further from the southern window so the light isn't as intense. As it is, a 3-hour period of direct light from this angle is not too bright, but since Aglaonema are adapted to moderate to lower light levels, you may find leaves look best in slightly less-intense light. You can experiment as the plant recovers (or with a new plant), bearing in mind that effects of light changes will only be visible on new leaves, unless older ones "sunburn" from over-exposure.

When it's ready for fertilizer, a general-purpose houseplant formulation would be fine; either liquid (liquid concentrate or powder diluted in water) or dry (granules/pellets), as per package instructions so it's not overdosed.

Miri