The adapter fits the Xiaomi Poco F7 to listen with wired headphones, as the Poco F7 does not have a 3.5 mm jack connection and has a USB-C port compatible with a digital-to-analogue audio adapter. The adapter converts the digital USB-C signal into an analogue 3.5 mm signal, which is required for wired headphones.
Yes, the microphone works with this adapter and you can also make calls as long as your device and the headphones or headset used support a microphone function.
To determine whether the coupling of the "Digital Audio Adapter USB-C to 3.5 mm AUX (Digital -> Analogue)" from Onit is 4-pin, we need to look at the technical specifications of the product. A 4-pin 3.5 mm connector usually supports both audio and microphone functions. Unfortunately, there is no direct indication in the information provided as to whether the adapter is 4-pin.
If the adapter supports both audio output and microphone input, it could be a 4-pin connector. Otherwise it would be a 3-pin plug that only allows audio output. For a definitive answer, it would be advisable to check the product description or the technical details directly with the manufacturer Onit.