@manfred Okay good to know you have already tried that.
So once you select an item in the left pane and click on edit at the bottom (pen icon) or create a new item (plus sign under left pane) the the following button will show up. This button is always present regardless of premium status.
@sj-bitwarden just messaged me and she was also able to reproduce and show me the same as in your screenshot. I now know how the confusion came up.
Attachments cannot be added directly to a new item. The item needs to be saved first and then within edit-mode the attachment button shows up. The reason being that we currently do not offer uploading attachments without linking them to an existing item.
Please try and add an attachment to an existing item, and this should work. The documentation states editing an item here.
thanks for coming back to me. The problem is still not solved. I re-installed the app and used an existing item but still to attachment option. I am in contact with support and hope they can resolve it.