Depends on what kind of struggle system mod we're talking.
EverDriven adds a classic "mash out of grabs" mechanic as part of its base kit, only you gotta beat the game to activate it.
There's also another mod that makes struggles more like BarbFTR and enhances grabs, BUT it's heavily W.I.P and the game cannot be beaten with it enabled as it only contains animations for Delta, Lambda, and Worm for now.