Q.What’s Wrong With Indoor Keylime And How To Remedy It, Part Two
Just adding the picture of the lime that left got out of previous post. This is the picture of the little Keylime that has lost a lot of leaves.

Certified GKH Gardening Expert
It looks like stress from lack of light, or lack of humidity. Both are very common, as these trees need full sun, and quite a bit of humidity. Indoor conditions lack both of these.
In fact, all of my indoor citrus remain under about 400 watts of quantum LED which is the equivalent of about 600 watts of sunlight. The more the merrier, with these.
Now, if you are just keeping them alive until you can put them back out, then you can keep them in the brightest window possible and spray them with water, daily. They will still lose most of their leaves through the winter, but they will stay alive in a semi-dormant state. They will appreciate just a little citrus feed every now and again, too.