Matter supports Wi-Fi and Thread for data transfer, and Bluetooth LE for commissioning.

Right now, Matter will support lighting & Electrical products (plugs, lightbulbs, switches, etc.), door locks, thermostats and HVAC controllers, blinds and shades, home security sensors (such as door and window sensors, motion sensors), controllers and bridges, TVs and media devices. Future iterations of Matter are expected to add support for security cameras, white goods(Appliances), energy management, closure sensors, wireless access points, environmental sensing&controls, smart speakers, robotic vacuums, smoke and carbon monoxide detectors, ambient motion and presence sensing. 

You could say yes, or not exactly. Since Matter has Multi-admin function, Matter devices can be controlled by all Controller apps, which means users can control all smart devices with just one app. However, this app may not enable all the features of the device. Some advanced features may not be available to Matter, such as power consumption on the socket, and complex effects scenes on the light strip. Therefore, users sometimes still need to download the device app, such as the meross app to set advanced features.

Matter is a new smart home protocol launched by Amazon, Apple, Google, and a host of manufacturers to eliminate incompatibilities between smart homes. Matter incorporates many of the benefits of HomeKit, such as a superb security protocol and a completely local architecture - no network connection is required at all. If you are an iOS user, you can use matter in almost the same way as HomeKit, simply by using the home app to do all the pairing and control. Since Matter is an open protocol, there will be a wider variety of products available on the market. 

Sorry, as Matter is a new protocol with different hardware and software requirements, most of the smart home products in the market cannot be upgraded to support Matter. The regular Wi-Fi and HomeKit products we have already released will not be able to support Matter by upgrading. We will release and develop new Matter-enabled products to meet the needs of our users. 

Multi-admin is one of the core features of Matter, as it provides for simultaneous operation in multiple smart home systems. Accordingly, family or household members could operate the device with the digital assistant or smartphone app of their choice. The last command given applies in each case. As an example. If a user has an Amazon Echo, a HomePod mini, and also wants to buy a Google Nest Thermostat. As long as the device supports Matter, he can add the device to both the Alexa and HomeKit ecosystems and even Google Home. Using any of them to control the device, the status will be synchronized to all ecosystems.

Security is a core principle of Matter, including the authentication of devices joining the network, encryption of messages to the destination, use of proven and standard cryptographic algorithms, and over-the-air (OTA) updates. Matter security does not rely on the security of communication technologies it runs on top of. Wi-Fi or Thread secure technology is an added level of protection.