I do not want to see the preview screen

There is a security problem.

Can I hide the preview screen from the upper right of the main screen?

there is a way to disable the preview of the images.
In doing so you will not be able to open the images on pydio’s interface you will have to download them and open them on your computer.

if you wish to you can go to Available Plugins > Editors > Image viewer and then disable it.