jsf67 said:Looks like a fern. Looks very much like it is the original contents of that pot (rather than a volunteer).
I can't see the resemblance to the specific fern linked above. But I don't have the fern you have nor the one linked, so I don't have much basis for distrusting the specific identification.
The ferns I have experience with are hard to transplant successfully (I've succeeded multiple times, but failed a much larger number of times). The ones I have experience with need a consistent good balance between sunlight and water, meaning they might grow well anywhere from 10% sunlight to 50% sunlight, but the amount of water that is too much (and would kill them) at 10% sunlight is way too little (again killing them) at 50% sunlight.
I would not expect any location inside an ordinary house to be entirely off the top end of its sun tolerance, so you probably didn't need to move it. Moving it to less sun just reduced the frequency at which it will need water. If I misunderstood you and the original location had no roof over it, then maybe (but nowhere possible on my own property) it had been getting flat out too much sun.
jsf67 said:Sorry I parsed your picture wrong. I thought it was a window between two different parts of indoors. I wasn't saying it should be indoors, I just thought it was.
Some of my own ferns are in direct sunlight for a large part of each day (less than half the day, but direct sun then, not dappled shade). Those are OK with some extra water.
Even once it is fully recovered, trying to transplant (to a different pot or to a bed in the garden) is a big risk. Moving the pot to a different place is not transplanting and should not be a big deal.
I forgot to comment on over crowded: In my experience, ferns do better when crowded. In my opinion, they also look better when crowded.