So...My Mini 3 was purchased from a 1st series released on market...
A few days ago was cold here, I have flied in mountain area, the inside lens become foggy after take off.

So, to clear a few things:
1. No Silica gel in world will help, as there is no fog outside lens...oh...and neither rice ))
2. Drone was sitting outside for 10 minutes, so all temperature was balanced
3. Inside lens fog is made only when cold outside air enters in sensor area that is very hot, the contact surface being the optics inside, that forms mist/fog.

As many presented on Youtube the problem and the fix, I have removed the case from camera...Surprise surprise... Not 1, but 2 O-rings (rubber in O shape) were in there, both not being far as O but as & or P....that chinese assembler was not drunk, but was both blind and without a hand, in order to "succeed" such a mizerable installation.

I have cleaned the rubber of both O-rings with alcohol, then applied a rehidrating agent for rubber....after 5 minutes the Orings had the correct shape of O regained, as they was squeezed to tight in there that was not even in P shape, but abstract one all over the place....

Both Orings were put in that plastic form for Oring...now....one thing important: if you try to put Orings one in other, will not stay, as both have same size...One is not enough as parts of Oring will suffer from squeezing and will not make full contact between plastic parts...so just turn one ORING at 180 degrees and put both ONE on top of the OTHER...The case will be closed a little forced, but you are 100% sure in that moment that air will not enter in sensor room anymore.

Problem solved, tested for 3 days in mountain area, with moisture and cold outside, no more foggy lens...

But, DJI...Fire that moron that assembled this all lot...and not to forget...your Quality Check stinks...a lot.

Your problem may be solved, but your warranty could easily now be null and void. If this is a manufacturing problem then the advice should be to return the drone keep your warranty in tact and let dji sort out their own mess.

Your warranty clearly explains that any tampering with your drone or remote will void your warranty, so first you do it at your own risk and if something goes wrong then may end up paying twice.
As you probably know there are posts on this forum from dji agreeing to replace drone for this problem, so is it worth the bother .

Maybe post a video showing what you done for those willing to take a chance because your explanation is not very clear and really shouldn’t be attempted without some video showing how you done it .

hallmark007 Posted at 10-3 02:30
Your problem may be solved, but your warranty could easily now be null and void. If this is a manufacturing problem then the advice should be to return the drone keep your warranty in tact and let dji sort out their own mess.

Your warranty clearly explains that any tampering with your drone or remote will void your warranty, so first you do it at your own risk and if something goes wrong then may end up paying twice.

Is already one on Youtube that shows it, no point to make another...
I have Care Refresh...also I would not stay for a fix from DJI as I can make it without being seen (just use a PH00 screw driver and be careful, will not remain any signs of tampering.
Still, if DJI comments, than can be forced to make a full action of recall for all drones, in order to fix them...I can also do that as European mechanisms can be activated at improper products very easy....
But my interest was to get drone fixed in a few hours as I was at a footage and some places were not for big drones but only for small ones.

I hope this will fix it (and hope DJI will too)

Geo…thanks for a good explanation and cure for the “foggy” lens problem. Well done indeed.

Hello there Geo_Drone. I am sorry for the trouble this has caused before and it is great to know that the issue was rectified and for sharing these information with us? In addition, these matter has been forwarded to the designated DJI Department for attention. Thank you.

There must be a temperature difference between the lens and the outside temperature!  
It can only fog up when the lens is colder...

Moisture never settles on hotter surfaces!

frankymusik Posted at 10-3 22:52
There must be a temperature difference between the lens and the outside temperature!  
It can only fog up when the lens is colder...

Exactly...as O-ring is not properly installed by DJI, and of course you know that sensor is reaching high temp on surface, is enough to enter inside lens some air from outside...as the air enters through O-RING that is not closing the gap, the lens surface INSIDE is getting a colder air, producing moisture...
Is simple fact...
O-Ring have the role to cut the airflow from outside and seal the sensor room, in order to not have moisture inside, but only outside (outside if you take the drone from very cold to hot, producing condensation outside the lens.)

So....O-ring fixed...Still, seems that there is a flaw in design...
Another day with cold morning, again, Mini 3 lens is toasted...I made the job with Mavic 3 and a Nano+, both not having issues, but I start to believe that is a problem with how camera is built, as some people here changed the drone a few times already and still get fog inside lens.
I send it today for another exchange, let's hope will get one that have no issues at least after 5-6 exchanges...