DJI Osmo Action 6 ND Filter Set
The one set DJI states fits the Action 6, with ND8, ND16 and ND32 and a case. It snaps on over the stock cover and DJI says that leaves waterproofing alone.
Install note
Read on DJI USA's product page on 2026-10-17: "Osmo Action 6 ND Filter Set", compatibility "Osmo Action 6", ND8, ND16 and ND32 filters and a filter case in the box, set dimensions 143.5 x 52.2 x 11.2 mm and weight 19 g. The page says snap-on mounting needs no removal of the lens cover and does not affect the camera's waterproofing. DJI's compatibility list ticks this set for the Action 6 and nothing else. Two owners of the set say on Trustpilot they use it on the Action 6 in bright sun and for water reflections; neither mentions fit. A maker-sold part: the link is not tagged and earns nothing.