Yes, jades are succulents, related to cactus. They need very little water. You didn't show a picture of your plant or say anything about what the soil is like. They need to be in good bonsai soil which is very mineral and free draining.
I don't know how you water, but you don't want to be getting this plant wet. It especially doesn't like water on the leaves.
But if it was doing fine before, and now is declining, that may well be related to less light in these shorter days. And if you have it sitting in front of a window, the angle of the sun changes through the season, so it may be getting less light due to that also. South facing windows are best for winter. It probably needs supplemental light - a dedicated lamp that shines directly on it from just a few inches away, as tom said on for at least 12 hrs a day.
These trees will shed a bit come fall and winter. They like to be on the dryer side with plenty of sun/ light. Also temps around mid 60's - mid 70's for winter. Water only when the soil is dry and give it as much light as possible.
Welcome to the Forum! Please keep us updated as to how your jade bonsai does!