As I've written - may be several issues - from the pump to the control module.

Is there no hydraulics at all?
Is there some additional hydraulics installed on the truck (sideshift)?
If yes - is it deactivated too?
If it works - this is probably a joystick issue.
So put the joystick from the extra hydraulics to the socket of main hydraulics. This will confirm the failure.

Is the motor pump working?
If no - probably you have issues with the hydraulics control module.
If yes - check the pump nad pressures before and after the control valve.

Of course - on the beginning, check the battery condition.
The truck may have the hydraulics "switch off" function, when the battery is too weak or discharged.

Unfortunately Linde developed this truck only to be diagnosed with diagnostic software.