I figured out that the hard drive, on which I installed Recalbox (old install before new graphic card), was taking the lead over the fresh recalbox that I was trying to boot from (a usb key). I think the SHARE partition of the hard drive was auto-mounted and used instead of the SHARE partition of the USB key.
It began to work when I disconnected the hard drive..
Thank you to the folks on Discord that helped and motivated me to troubleshoot this.
