I’ve been trying to add, for the past couple of years, some Nanoleaf Essentials bulbs to HA. They are connected via Thread to my Google Home Hub and the Hub is my ‘preferred Thread router’ in HA.
Unfortunately these bulbs are NOT Matter devices as I have no problems adding my Nanoleaf Matter lights.
They show up as Homekit Devices and it wants the Matter xxx-xx-xxx format but trying the 8 xxxx-xxxx digits in both Thread and Matter formats fail.
Has anyone solved this conundrum ?
I do not know HomeKit, but for Matter devices you can only use the QR code on the device for the first pairing after a factory reset.
After that you need to get a sharing code from the Matter hub it is connected to, to share it with another hub.
As in my O/P, these bulbs are Thread devices, but they were before Nanoleaf used the Matter standard. I have no problems with adding their Matter lights.
And tbh I don’t know Homekit either as I’m not it the Apple world.
Ok, I managed to make it work.
I just happened to have bought an ESP32 this week and saw it could be a BT proxy.
I reset the bulbs and they appeared as a Homekit device, I added using the xxx-xx-xxx format.
Bam, added to HA 
I was then able to tell the lights to join my Google Hub’s Thread network.