Shadow on the moon

Answer

Satellites don’t create a shadow that extends to the surface. So it couldn’t have been that. I did the math once, a satellite with a size of say 3 meters would make a shadow cone of about 300m. That is the ratio of size to length of the shadow cone at a distance of 150 million kilometers from the sun. The sun there has an apparent diameter of half a degree.
Satellites around the moon are at least a few tens of kilometers to stay over the highest mountains. And satellites orbiting the Earth certainly won’t cast a shadow on the moon.
Was it a satellite that revolved around the earth and happened to pass between you and the moon? That can happen in itself, but you won’t see it. A satellite is only a few meters in size, and is located at an altitude of many hundreds of kilometers. At that distance you can no longer see such a small object.

What have you seen now? In science, we always look for the simplest explanation, and I think of a plane you saw moving over the bright lunar disk. That can indeed take a few seconds depending on the direction. That is the most obvious explanation that agrees with your observation. The statement that requires the least additional assumptions.