On the homepage I build with Visual Composer an overview of projects. The portfolio title and category are shown. Is it also possible to show the excerpt and maybe hide the categories?
This feature is not implemented however I can help you achieve this. You need to replace one template file in Kalium files. I suggest you to use child theme in order to not lose changes when you update Kalium.
Download this file and replace it in this directory (of the theme): /tpls
(view large version)
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I've uploaded the file in the child theme folder, in the directory /tpls. Do I have to activate or select the portfolio-loop-item-type-2 in the admin (portfolio item element)?
Yes, thats the correct path to upload. You don't need to do anything else because whenever you use portfolio with titles inside thumbnails it will automatically show the excerpt. Did it worked for you?