In Youtube videos describing how to attach filters to the Mini's camera, it's recommended that you do so while the drone is turned off, so the gimbal doesn't "fight" you. When it comes to CPL and ND-PL filters that need to be rotated before flying, it's advised to do so while the drone is turned on, because it's easier to figure out the perfect angle while watching the effect on the video feed.
When adjusting the filter with the drone on, you still need to hold the gimbal while rotating the filter. While doing so, you can still feel the gimbal trying to move. Is this safe for the gimbal ?  Finding the ideal angle by powering the drone on and off would take a lot of time.

I would be very gentle if I left it on. But, basically, there are two positions for a CPL. 0 or 90 degrees. It doesn't take that long to try the two. And then at 45 if you want to. Either remember the effect or make a reference card for future.

Hello there cpper. Good day and thank you for sharing these information with us. Since this is a 3rd party accessory ( ND Filters ) for the DJI Mini 2. I hope that you will get the best recommendation from our fellow DJI co pilots who have used the said filter on there DJI Mini 2 DJI Drone. Just a reminder that DJI does not recommend you to your 3rd party accessories like ND filters on your DJI Drones. These 3rd party accessories might affect the said DJI drone when in use and there is a possibility that these 3rd party accessories will be able work. However, since it's not optimized and tested by DJI we cannot guaranteed the stability of the said 3rd party accessory if it will work all the time with no issues and might damage and void the warranty of the said DJI product. Thank you.

To adjust the CPL filter angle on a DJI Mavic, follow these steps:

Place the CPL filter onto the camera lens with the polarizing element facing outwards.

Turn on your drone and enter camera mode.

Look at your live feed to see if there is any glare or reflections in your shot.

Rotate the CPL filter until you see a reduction in glare and reflections.

Adjust the angle of the CPL filter as needed until you achieve your desired effect.

It's important to note that adjusting the CPL filter angle may affect exposure and color balance, so be sure to monitor those settings while making adjustments.

lazysk8r2 Posted at 3-9 19:11
To adjust the CPL filter angle on a DJI Mavic, follow these steps:

Place the CPL filter onto the camera lens with the polarizing element facing outwards.

Adjust the angle of the CPL filter as needed until you achieve your desired effect.
That's fine, but what you've not mentioned is that it's only good while the drone is pointing in that direction.
Turn the drone to face somewhere else, and your polariser is not working properly and is probably giving you a weird blotchy sky.
Polarisers on drones are more trouble than they are worth.