Hi @PedroHamzeh,
I do not know of a way to export/import more than one course at a time since you have to select an import file and export from a single course. Are you wanting to export multiple courses because you want to import select parts of the course or are you looking to import the full course content and have one large course with everything? You could also use the Copy a Course option where you can select the specific items you want to copy over into your new course.
Depending on what you are trying to do you might have better luck with Canvas Commons. If you are wanting to pull resources from multiple courses and get them into one Canvas Commons might be better suited for that vs the export/import option. Your institution does need to have Canvas Commons turned on. The below resources might be helpful.
What is Canvas Commons - Video Overview
How to share content to Canvas Commons
How to import and view content from Canvas Commons