Just so I am clear, am I right in saying that we can directly connect this device 샤오미 게이트웨이 애플 홈킷 | Smart Home Kit Zigbee Xiaomi | Xiaomi Smart Home Aqara Kit - Door - Aliexpress to the smartthings V3 hub?
My understanding is that if something is compatible with Matter (not with Matter thread), then it should directly pair with ST V3 hub without any additional device?
Did you read the second post in the Matter FAQ thread? It details exactly what you need to use different kinds of matter devices with SmartThings. Devices might be individually certified for matter over Wi-Fi, individually certified for matter over thread, or not certified for matter but work with a matter bridge. Those are three different situations with three different requirements.
You quoted me talking about matter over Wi-Fi, but you linked to a Zigbee device, which would have to work with a matter bridge.
Also, I suspect that the specific offer you linked to is either counterfeit or a reseller who doesn’t understand the technical specifications for the device because they are using pictures that don’t go with the product description. The pictures have the matter logo, but for aqara, that is only true for the thread versions. The product description says it is a Zigbee device, and those are not individually certified for matter, they would use a matter bridge.
(By the way, aqara will not provide warranty service for anything bought on AliExpress because there are so many problems with counterfeits there, or defective items which were returned to another seller and then sold as new by a reseller. )
So the answer to your general question is no, that’s not how matter integration works. Read the second post to see what the requirements are for each of the three different types of matter integrations.
And the answer to your specific question about the device that you linked to is that there is no way to tell: aqara doesn’t have any Zigbee devices that have individual matter logos, so something is wrong with the product listing. 
Thanks JD and yes I did read your first post but I thought this device would work as it had matter logo in it as per this screenshot.
So, how about this one COOLO Matter Smart Light Bulb RGB E27 Wifi Led Bulb Smart Home Works with Alexa Google Home Apple Home Homekit SmartThings Siri (aliexpress.com)? Will this pair with ST with a matter bridge?
I am not going to buy anything but in case I want to buy something in future, I just want to know what to check for hence the ask.
As I said, in my previous post, that’s an unauthorized seller listing and the picture doesn’t match the product description. For the product they describe in words it should not have a plain matter logo on the picture. Or a HomeKit logo. So that’s a problem with the listing, not the product. Unfortunately, that happens a lot on the aliexpress site. 
So, how about this one COOLO Matter Smart Light Bulb RGB E27 Wifi Led Bulb Smart Home Works with Alexa Google Home Apple Home Homekit SmartThings Siri (aliexpress.com)? Will this pair with ST with a matter bridge?
As the second post in the Matter FAQ topic says, if the device is individually certified for Matter over Wi-Fi, it will not require a bridge.
Personally, as I have mentioned in other threads, I don’t buy lightbulbs that don’t have UL or ETL or TUA safety certifications. But that’s just me. 
What should it have then? how can I find out if it’s matter over Wifi? Also, though it says matter over Wifi, I am assuming it will not directly connect to the router but instead it will connect to the ST hub?
Matter over WiFi devices must connect to your WiFi router, that’s the way they send their messages. What they don’t need to connect to is the Internet. (Internet and Wi-Fi are two different things.)
The Matter over Wi-Fi device communicates with your SmartThings/Aeotec hub using the Wi-Fi network in your home. That Wi-Fi network will be managed by your Wi-Fi router.
As far as what the product description at AliExpress should say, you need to understand that AliExpress is just a marketplace for thousands of different individual vendors, most of whom don’t know anything about the technical aspects of what they are selling. (And they often get their goods from returns auctions, or used.) They just copy and paste pictures and descriptions From other places to make their listing based on what they think they have at first glance. So a lot of them get a lot of things wrong.
It’s just too exhausting for me, literally, to go step-by-step through that kind of mosaic.
If you want to ask questions about a matter device, Please find a link to the manufacturer’s official description, either on their site or an authorized reseller.
Or if you want to talk about a specific aliexpress listing, please take it to a different thread than this one. It’s going to be way too specific to fit a FAQ discussion and I won’t be able to help with it anyway. So feel free to start a new thread for that and other people can help you.
Thanks for your detailed explanation by the way.
I have a limit of 28 devices in my router so matter seems to be a non-starter as I already have 28 devices. I have tried adding 1 more device but it doesn’t get paired regardless of whateve I try to do so I understood the limit was 28. So, should I have to buy a repeater if I need to accommodate matter over wifi devices?
But if you are saying that matter over Wifi needs to connect to my router, then I am stuck right as my router does not allow to connect more than 28 devices?
So, I need to move some of my Wifi devices to matter devices or go with Matter over Thread in which case I will need a thread border router?
I’m not sure I understand your question. You don’t move Wi-Fi devices to matter devices. Wi-Fi is the transport network protocol. Matter is a way of defining the messages that will be sent.
Matter devices can either be matter over Wi-Fi, matter over thread, or matter over bridge.
In your case, you have a problem because matter over Wi-Fi devices have to make a Wi-Fi connection. Matter over thread devices need a thread border router, and the thread border router has to make a Wi-Fi connection. Matter over Bridge devices Connect via bridge, and again, that bridge has to make a Wi-Fi connection. So regardless which of the three matter methods you use, you have to be able to add another Wi-Fi device.
The only possibility would be if you already have a Wi-Fi device connected that already acts as a thread border router. That could be most of the Alexa echo devices, a number of Google home devices, an apple HomePod mini, or even a SmartThings hub v3. In That situation you would be able to use matter over thread devices.
I should have read your first post properly. I am having a v3 hub so I don’t need a thread-border router so I will buy matter-over-thread devices. Thanks.
