The diameter of the turntable is 28.50 cm. The maximum diameter is about 30 cm. After that it gets tight because it is difficult to place the plate exactly in the middle.

That's right. The accessory pan for pizza and steaming is approx. 27.5 cm.
By the way, I can only recommend this appliance. I recently bought one myself. Simple, with good instructions that simply explain how the appliance works. It also has an explanation of how best to prepare food and also how the appliance should be set and also for how long.
You can grill, steam or simply microwave.