Statistics

How can a non-linear regression to calculate the statistical R-square,
R-square adjusted, RMSE, VIF??

It is not clear that these statistics are meaningful for a nonlinear
regression model.  For example, an R^2 value is meaningful when the
model being fit contains the constant model because it compares the
fit of the current model to the fit of the model y ~ 1.  Not all
nonlinear regression models contain the constant model as a submodel.