We were on ' Natural Greenland ' 10/7/22 to 31/7/22 cruise that I believed you mentioned in an earlier posting.
We have also been on SoD in September 2019 and there was no soot problem.
This year we were on SoD 'Northern Lights ' in March, we didn't notice any problems until disembarkation day, when due to late arrival into Southampton I was up on deck 13 when I noticed my cream jacket was marked with smuts, I was not the only person to comment on this.
On the July cruise, we repeatedly noticed smuts on all of the upper aft decks to such an extent that we couldn't use the handrails as they left your hands filthy.
To obviate any doubt as to the source, this includes sea days with no other shipping in the vicinity.
The cleaning crew said the smuts were a daily problem, indeed as some of your photos show of the decks drying from recent washing.