Hi, I would like to know if it is possible to add Threejs 3D products/product configurators on Solidus and what approach should I follow fo such an implementation.

You definitely can. Once the configurator is ready, as output it should give a variant and probably a set of options (which represent that specific cusomization) to be added to the cart as a line item. You can add it to the cart using this controller: https://github.com/solidusio/solidus_starter_frontend/blob/main/templates/app/controllers/cart_line_items_controller.rb#L11 or with the https://solidus.stoplight.io/docs/solidus/a5401c50bbfc9-create-order-line-item endpoint if you are building your storefront with some JS framework.

Thanks!