Cleaning: What is the problem causing this ring-shaped artifact in my image even though I have cleaned my lens?

Based on its shape and brightness profile (glossy edge, center of attenuation) and the fact that it is in the same location in various frames, I think this is a dust of dust on the sensor.

If your camera has a removable lens, and you can lock the mirror (assuming you have one), you can probably use an air bulb (I think they are a negative blower, because I learned from the movie) to remove dust. Acknowledging, of course, the risk of it just moving it, or even allowing it to settle there.

If that doesn't solve the problem, sensor cleaning kits are available from the largest online photography stores. READ AND FOLLOW THE INSTRUCTIONS and also consult the manufacturer of your camera (or at least the instructions) to avoid possible damage to the sensor. The same rule applies to cleaning lenses: NO. Yes absolutely should, do it as gently and carefully as possible. A damaged sensor is a destroyed camera body …