Same problem here. Somebody knows how to override correctly twig admin templates for last Prestashop versions (1.7.6.x)?
If I understand right, you have to create a module and copy twig template files at views/Prestashop/Admin/Product/Forms/form_products.html.twig, for example, and then modify file to insert custom hooks, add new contents or wathever you want.
But my question is... simply coping templates files to correct path inside your module folder, and activating module is enought? You don't have to use any hook or other method to make know that you want to use modified templates instead of original ones?