Saw some video on youtube (quite a lot) where this warning/error is showing up. At first i though,  oh that's because he is flying over the water, so the sensor went crazy, cannot determine distance because reflection. Then i saw this warning showing while drone was flying close to ground or in the air but with ground (land,forest, trees) downward. Can someone explain better the reason that cause this to appear ?

Are you talking about my drone is going to crash into a tree or ground warning (which is normal) or a my downward facing sensor is not working error? Can you provide a screenshot or be more specific....

Hi, low light is a big factor

here is one from youtube user https://www.youtube.com/c/DutchMarkyMark  during a test flight,

Hello there Mat8861. I am sorry for the trouble this has caused and thank you for reaching out.  Just a reminder that the DJI Mini 3 Pro's vision system cannot work properly over surfaces that do not have clear pattern variations. The vision system cannot work properly in any of the following situations below. Please fly your DJI Drone cautiously. Thank you.