Please provide the possibility to zoom in / open a pop-up window for all (product) pictures in CMS and especially those on the "Media" tab
This is not an Episerver question, but more of a front-end implementation.
There are many JS frameworks out there to help you to achieve this. Choose the right one based on your implementation.
It feels like your asking for a DAM or do you mean by default inside the Episerver editor?
He means in the editor I think, as the thumbnails are quite small, so it could be difficult to find the correct image
That is correct, this is for the Catalog view where we can see the thumbnails. It is too small and the user does not want to click on the product, go to the image tab and view the full image. This is very time consuming.
Grzegorz Wiechec made an extension to the media pane where thumbnails are shown bigger and optionally as a grid.
You might want to take a look at this: https://gregwiechec.com/2018/11/media-gallery/ (although I'm not sure if it works for the product catalog).