There is no information about this on the Captiva homepage. The only thing is that the mainboard has a second m.2 slot and 6 SATA ports. It may have a possibility to mount an SSD at the bottom next to the power supply. You can check here: service@captiva-power.de or buy the PC first and see if there is a possibility to install an SSD/HDD. If there is no possibility, I would recommend an external solution. Fixing the HDD with adhesive tape is not an option; it is too heavy and vibrates too much. SSD is OK in an emergency.
If the mainboard still has a place for it, definitely. You will probably have to attach it with adhesive tape or not at all, as there is no predetermined space.