Hey there @Edea,
I see what you are going through. You should share your store URL so I can take a look at the error and the source of error so I may be able to help you or give you a direction.
Hey again @Edea,
I see the error, that's probably because you messed up with the theme.js or cart.js file. You probably deleted (or modified) the script to add the product to the cart. There are some more issues too like the dropdown in the menus not working etc. I can help you with it but it will require taking a look at the backend. Contact me if you need my help.