Can I integrate Miele appliances into a mesh WiFi network that switches automatically between 2.4 GHz and 5 GHz?

Yes, you can.

A mesh WiFi network automatically assigns the frequency band of 2.4 GHz or 5 GHz to the terminal device. In accordance with the IEEE 802.11 standard, the appliances disclose the frequency bands that they support to the access point.

The access point assigns a suitable channel with the relevant frequency band to the appliances and they can be integrated into the mesh WiFi network.