Hah, I have an AC window unit from Miele that is a great piece of hardware. But the app, my god, it's so bad. Every launch of the app requires a log in. Every log in error messages pop up about api endpoint such and such, but it works anyway. If a command fails, which it does half the time, the app gets out of sync with the unit (i.e. app will say fan speed medium, unit will say fan speed low). So I guess it syncs state on startup and never again, and doesn't check if commands fail. But there is one feature I can only find in the app, not from buttons on the unit (turning all LEDs off on the unit while it continues to run).
The buzzwords I never hear on HN is Digital Twin. It's usually in a HVAC or like smart building context. It's a buzzword for a simple idea, but the makers of the Miele AC app probably should have thought a little harder about tracking system state, maybe read a little of the literature.