UPDATE: I'd like to say now I know what I'm doing but I would be telling a fib.
I have now got an Aqara M100 Hub purring away in my wifi home network. over the weekend, I acquired a 'KAJPLATS' E27 bulb which came with a 'BILRESA' 2 button switch, both of these being Matter over Thread devices.
This was where the fun started as I simply didn't understand what role the M100 was playing in the set-up. Pairing them directly to the M100 was a piece of cake but then the first of many pennies dropped that there is no way to "include" the M100 in HE in order to get at the newly paired devices.
So, the new devices got promptly "unpaired" from the M100. I read that I should be able to pair the new Matter devices directly in HE and this is where I made just about every mistake you can think of whilst attempting this. I run a VPN on all my stationary and mobile devices and and after reading that these should be disabled during pairing, I dutifully did this. But still no luck😔
I then continued my attempt to pair using my stationary pc and, of course, I was getting nowhere. Second penny dropping was that I should have been doing the pairing via the mobile app but still no luck😔
I continued to have no luck pairing anything until another one of those pennies dropped when I realised I did not have IPV6 activated in my router, So a bit more "settings" were twiddled with in the admin pages of the router.
More rereading the installation advice and the fourth penny dropped as I realised my mobile usually uses the 5GHz wifi channel at home, so I switched to the 2.4GHz channel. Then things started to happen!! I registered both the bulb and the button unit successfully. It was during the inclusion of these devices that you are flashed a message telling you the thread border router is being checked into and confirmed. This is the only time you are even given a clue as to what role the M100 is playing in the set-up. But after successful registration in HE, I could now apply my control rules and button controllers and I finally had Matter devices playing their part along with my numerous Zigbee devices. Even using zigbee devices to control Matter devices. Cool stuff.
And if i open the Aqara app, I just see the M100 in the device page and none of the HE registered matter devices are present. So my assumption here is that this is what is meant by the M100 acting as a Thread Border Router and not a Thread /Matter controller. I don't know whether the M100's 20 Matter device limit is even relevant here but I'm unlikely to exceed that anyway.
So to recap, my wish was:
- To be able to control Matter devices from HE.
- Owning none of the mentioned devices that can act as TBR, I needed to acquire one.
- I buy the Aqara M100 for very reasonable price.
- Set up M100 as per instructions.
- After quite a few 'hurdles' regarding settings and method, I can now attach matter devices in HE and once they're in, the sky is the limit.

Sorry for this bloated post but I felt the need to write something here should another lost soul run into difficulties regarding Matter, Matter controllers, Matter over Thread, Thread over Wifi, Thread itself, Thread Border Routers and so on and so forth:wink: