If I use… let’s say no retreat as a plus move, what will it do? Decrease cool-down? Some other effect?
There is no universal answer for every status move. Some, like Aqua Ring, have a lower wind-up time; others, like Amnesia, have an increased effect duration; some, like Toxic Spikes, don't change at all.
For your example specifically, No Retreat has its effect duration increased from 15 seconds to 18 seconds when turned into a Plus Move.
List of moves in Pokémon Legends: Z-A (Bulbapedia)
