I am pretty sure P9 introduced non-lethal attacks, I had taken a break from the early access around P7 wanting to wait now for the full game, so it may have been added before but I am pretty sure it just got added.
The use of non-lethal attacks, however, breaks continuity in many quest lines and needs further development. Example, you meet Ethel and the two brothers arguing in the woods, failed dice rolls leads to a fight with the brothers, you switch to non lethal and knock them out. Does the game recognise this? No, it records the two brothers as dead and now you can inform the sister you killed her brothers or try trick her into thinking Ethel killed them. All the while the two brothers are forever lying out cold in the woods. I am sure there will be lots of examples of this happening in quests now and it is something that I think Larian should address to make everything make more sense and fulfill immersion.
Firstly, the game should know when we chose the non lethal approach in quest lines and instead of telling sister her brothers are dead we can tell her there fine, a slight headache but fine. Further, new dialogue should be possible with people who have been knocked out. Some NPCs should get up and move on, these two should realize they can't win a fight against my party, apologies and beg for help, which we may very well give after seeing poor old Ethel suddenly teleport away. This will also require a mechanic by which those knocked out eventually wake up, either after a certain number of turns, or after the player uses the help ability on them like with down characters and defiantly after rests. After a long rest, at least, these guys should have moved on back to the grove where we could, perhaps, eventually return their sister to them despite the disagreement.
This does seem like it would be a lot of work, adding a lot more dialogue and interactions for the many questlines this could affect, but unless Larian do that, what really is the point of the non lethal mechanic?
