Yeah, this is a common ask, but it's outside the intended use. Officially, no. The machine is intended for driving screws and drilling in wood, metal, ceramics, and plastic. Using it for mixing thick substances like paint or mortar can overstress the motor and gearbox.
If you try it anyway, you're risking it. The maximum torque is 40 N.m, which might not be enough for stiff mortar. You could stall the motor or cause internal damage. The tool isn't rated for continuous operation in its variable speed range either—that can damage the switch.
Heads up: Forcing the power tool or using it for operations different from those intended creates a hazardous situation. If it gets damaged, you need a qualified repair person using DEKO replacement parts.