Planets are not stars. On casual observation, both planets and stars appear as bright dots in the night sky. But with careful observation, we know planets are different from the stars.
Flat-Earthers insist that planets are just stars. In reality, we can easily observe many of the planets’ attributes that set them apart from the stars —using minimal efforts and equipment.
Stars appear to twinkle, while planets do not. This is caused by the fact that planets have a larger angular size than stars. The air motion in the atmosphere bends starlight; sometimes, it reaches us, and sometimes it does not.
Planets have different movement than the rest of the stars. They appear to shift day by day, relative to the rest of the stars. We can easily observe this by observing a planet’s position relative to the stars for several days.
Some planets have visible satellites orbiting them. Jupiter has four satellites, and it is easy to observe them with only a cheap telescope or binocular.
Some planets have distinctive features. Saturn’s ring can be easily seen using a telescope or a long-zoom camera.