Hi, I'm new. I'm considering buying the Mini 3 (NOT PRO).Can you mount filters on it? Do I need them? I would only shoot STILLS, NOT VIDEO.
Also I'd like to ask if I can change the aperture on the drone (I know it's a 1.13 inch sensor, just asking).

Hello, there. You can mount filters on the gimbal. Steps are below:
1. Hold the gimbal and camera module, rotate counterclockwise in this position, and remove the original lens cover;
2. After removing the original Lens cover, there will be raised clasp;
3. You can judge the front and back of the dimming mirror by the word ND on the outside, when it is upright, "NDxx" is directly above;
4. Aim at the correct installation port and rotate clockwise in this position to complete the installation of the ND filters.

You may make the decision based on your needs.
DJI Mini 3 does not support changing the aperture.

"Do I need them? I would only shoot STILLS, NOT VIDEO"
For stills you may use ND filters for long exposure effects, sometimes used on things like waterfalls and waves.
You may also want to use Polorising filters to cut reflections and glare.
They are not necessary for stills, but it depends on your particular needs, if you intend on these kinds of effects.

In video ND are widely used to reduce shutter speed. With a fixed aperture the shutter can be quite fast in bright conditions, which can make movement a bit choppy with no motion blur.