In contrast to the PC-12, the PC-24 does not have a standby battery or standby bus switch in the overhead panel. The lower DU will start with all the other screens when you switch on the Bat 1 and 2 switches in the real plane. It’s a Carenado bug like so many in this plane.
P.S.
However, this may not be entirely correct. In the video i saw, the Gen1 and Gen2 switches were already on when the pilot switched on the batteries and external power was available (although probably not switched on).