// MouseHandlerMixin.java
@Mixin(MouseHandler.class)
public class MouseHandlerMixin {
    @Redirect(method = "turnPlayer", at = @At(value = "INVOKE", target = "Lnet/minecraft/client/player/LocalPlayer;isScoping()Z"))
    private boolean slowCamera(LocalPlayer clientPlayerEntity) {
        return clientPlayerEntity.isScoping() || AdditionalAdditions.zoom;
    }
}

// PlayerMixin.java
@Mixin(Player.class)
public class MouseHandlerMixin {
    @Inject(method = "isScoping", at = @At(value = "RETURN"), cancellable = true)
    private boolean slowCamera(CallbackInfo info) {
        if (AdditionalAdditions.zoom)
            info.selReturnValue(true);
    }
}