Your bonsai is a ginseng rooted ficus tree.
I'm pretty sure it is not getting enough light and it is staying too wet around the roots, but not humid enough around the leaves. Avoiding direct hot sunshine is one thing, but your tree is barely getting any light. The no direct sunshine is for outdoor trees. Indoors it needs pretty much as much light as you can give it. If you have a good south facing window that gets lots of light, that would do. Otherwise it needs supplemental lighting - a dedicated fluorescent light that shines directly on it from just a few inches away, that is on 16 hrs a day.
The leaves need to be misted daily and/or it should be on a humidity tray. This is a tray you put water in and pebbles. The pebbles support the bonsai pot so that the pot is OVER the water, not in it. The idea is just to add some humidity around your tree.
It doesn't look like good bonsai soil which is very mineral and gritty and free draining. In the spring you should re-pot into good bonsai soil. For now just be very careful about watering. Do not fertilize at least until it is growing new leaves again.
Here's a thread with lots of basic bonsai growing information, including how to water: https://www.helpfulgardener.com/forum/vi ... =36&t=1479
Here's an article with a lot of information about bonsai soil
It is a living tree and needs what trees need. If you just want a desk decoration and aren't prepared to give your bonsai daily care, there are lots of really nice artificial ones.