Is there any martial arts activity at fenix 6

Martial arts with watch on your wrist sounds not a good idea. Unless you are talking some  karate  kata. I would suggest not to use watch in full contact sports.
On another hand what benefits you want to track ? heart rate ? ( put cardio on and you are done :) ) Keep in mind  wrist  heart rate monitors are not  accurate while you throwing your hands around.

Indeed, I don't think I would recommend using an $800 big hunk of sharp-edged stainless steel as your activity tracker during martial arts.

If I did a lot of martial arts, I would get something like a Vivosmart HR to use for that - no sharp edges to cut yourself/others with, lightweight, and cheap enough that you won't have to sell one of your children if it breaks. After the activity, put it back in the gym bag and then wear my Fenix again.

If you must wear your Fenix, just use the Cardio activity. I'm not sure what all you are hoping to "track" with your watch during martial arts - number of karate chops? It seems to me like the only useful metric worth tracking would be HR, calories, etc. Cardio activity does that just fine. If you want to it be called "Martial Arts", then just make a copy of Cardio and rename it "Martial Arts".

Or you can use a Garmin strap and download the HR data after the workout.

Yes i would use garmin heartsensor or polar oh sensor when measuring heart rate. 

I waa thinking theae algorhytms which are inside  theae activity moduls.

Boxing calorie counter differs aiot from cardio.