How do you use an ND filter for your 360 camera? One way is to use a rig….
Paulo Teixera shared this video by Personal View, where SLR Magic shows their filter system which attaches to rear lenses of Micro Four Thirds lenses:
Technique: using ND filters for 360 cameras

I use ND filters on my Freedom 360 rig. Very useful! A lot of times I use filters on the top 3 cameras and not on the bottom 3. This helps with the over-exposure on the sky.