Data augmentation solutions for tabular/structured data Are there any reliable libraries or methods for tabular/structured data (with numerical and categorical features) augmentation? Could you share some?

Basically I believe inventing/augmenting more data could help to improve model performance.
It's hard in general, because you don't know the joint distribution of the data, let alone joint distribution with the label -- or else you wouldn't need a classifier. Without that you can't confidently sample new, valid instances.

In the image case it's 'easy' because we know certainly that a rotation or shear or scale of an image produces another valid image, and we know its label is the same.

If you're willing to make the assumption that points in your input space between two instances with the same label are also a) valid inputs and b) have the same label, then you can apply things like SMOTE (https://imbalanced-learn.readthedocs.io/en/stable/generated/imblearn.over_sampling.SMOTE.html) to generate more data according to that assumption. If that assumption is wrong, it'll hurt performance.