Thanks for the tip, I had never heard of nested virtualization. That must be the problem since VirtualBox doesn't let me enable nesting and there is no setting in the BIOS. I'm testing on an old ultrabook with a Core M-5Y10, I guess that's the limitation 😅😂.
I did some research and it's not very clear which CPU allow nesting, is it a feature reserved for Xeon?
Edit : I answered myself, I checked on my wife's i5 9600K computer and I can activate nesting 👍.