How do I make my gun push the player opposite of aiming?

i have a platforming game with a gun that points at the mouse, and there's an upgrade that pushes the player back where the player is aiming opposite, if the mouse is at 90 degrees of the player, then the player would move left a bit. This would also apply to aiming up in the air, and down on the floor.

The easy one is by utilizing 'impulse' in physics behavior.

I'm assuming you use platform behavior?

would the force variable be jump strength?

The force variable can be whatever you want it to be. If you want the knockback to be tied to the characters jump strength, then yes.