Stars are so far away that they look almost like point sources of light. Any small atmospheric distortion is immediately visible.
Planets are also very distant, but through a telescope they appear as tiny disks rather than mathematical points. Their light reaches us from different parts of that disk, and the atmospheric fluctuations partly average out. That is why Venus, Jupiter or Mars usually shine more steadily.
Close to the horizon, however, even a planet may twinkle noticeably because its light passes through a thicker layer of atmosphere.
There is a simple clue: if a bright “star” is barely flickering, you may actually be looking at a planet. Sometimes the sky tells us what we are seeing - we only need to hold our gaze a little longer.
The stars speak. You decide.