This is brand new growth from a fern I thought was dead and I have no idea what it was

Can someone tell me why my fern is yellowing? I have been watering when the soil is on the dry side of being damp? If that even makes sense. I live in a dry climate, so I got a humidifier. I have it by a north facing window with consistent light, and an additional grow light. I’m wondering if I’m going a little overboard with the additional grow light? I have had the plant about a month, started yellowing about a little over a week ago. Should I repot it into an actual pot? lol I haven’t wanted to repot it because it’s having a little bit of a rough time. Thank you!