Hey Bonsai Empire,

My name is Ryan, long time bonsai enthusiast but new owner of my first bonsai.

I received a Chinese Elm for Christmas and have kept it indoors since then directly adjacent to a window with decent light.
Initially the bonsai was doing well, leaves appeared healthy. Then during an abnormal heat spell mid-winter the tree had a lot of new growth and new buds. Now that the weather is back to typical winter with mostly overcast skies the tree has shriveled up significantly and dropping leaves.

I’ve been researching the care guide and I’m not sure how worried I should be.
I attached photos of my bonsai in its current state.

Current Setup:
The pot has good drainage holes and is placed on a tray that can retain excess water to act as a humidity tray.
I’ve been very careful to check the soil before watering (which currently has been about once a week).

My big question is:
Am I overwatering or underwatering?

Hard to tell with no pictures attach.

Let the top soil become dry and then water. The soil needs to become dry between watering but not completly dry. You can use a chopstick and put it down into the soil. Take the chopstick up and see if it's wet. If not, water it.

Put you bonsai outside in spring and let it stay outside all year around with winter protection. Thats best for your elm.

Sorry I thought the pictures had attached.
Here they are.

Hello, welcome here.
I think the leaves on your Elm look too dry, which leads me to watering thoughts.
My Elms in Brazil right now, in the summer, outside, they really need plenty of water twice a day.
But this info has no use for you if you are in the Northern Hemisphere.
They need light, they need water, they need air movement, and they don't like sudden temperature changes.
Otherwise, they are easy to grow, even indoors (plenty of light!).