Question about Xiaomi Smart Air Purifier 4 Pro

The devices are compatible with Android and Alexa, but not for Homekit. Apple is very limited with Smarthome, not many products are compatible, but the Air Purifier 4 can also be operated in automatic mode, it does not need a connection to an app. You can make all the settings on the device itself, I would recommend the automatic mode anyway, because then you are also sure that the air is always cleaned.