The Wi-Fi adapter for the Miele appliances only supports pure WPA2 encryption.
WPA3 encryption and mixed operation using WPA2+WPA3 encryption are not supported.
Change your router settings to WPA2 encryption. Consult your Wi-Fi router’s operating instructions for additional information.
The system requirements for Wi-Fi are available in the article at Miele@home > Miele app > System requirements for Wi-Fi.