There is another connectivity as ZigBee and Zwave. It is called Thread. You can find it on some google, amazon and apple devices.
We have guides for building up a router
But we don’t have the integration or the addon for do that. Vote please.
The latest versions of the Silicon Labs Multiprotocol container (see addons-development/silabs-multiprotocol at master · home-assistant/addons-development · GitHub) comes with OpenThread Border Router configured. So in a way we have such an add-on. I am working on a more generic variant of it.
That said, Thread is a mesh protocol which enables IP(v6) over IEEE 802.15.4. It by itself is not really useful for Home Assistant, as an application level protocol of some sort is needed to control something or get information from something. With the above add-on, you can on-board and ping a Thread device, but now what? 
We have the addon!!!
It is on this repository:
I’m delving more into Matter/Thread/Zephyr now.
I’ve had my nrf52840-dongle for awhile.
Does the option exist to communicate with 802.15.4 devices using Matter through the dongle from home-assistant from an Android device (think bluetooth, since the dongle doesn’t have 802.11)?
Looking at NCP(apparently nordic is discontinuing ncp)/RCP, I’d wonder if you could just use the dongle and not require anything else like an rpi/pc.
If going with NCP, I’d imagine (Android phone or PC (via bluetooth) → dongle (via Matter over Thread) → any 802.15.4 device)
With RCP, it sounds like it’d have to be (Android phone or PC (via wifi/bluetooth(if BT possible)) → rpi (via Spinel) → dongle (via Matter over Thread) → any 802.15.4 device).
NCP sounds much better, as it wouldn’t be reliant on anything else.
I know Espressif has their esp32-c6 in the pipeline which does 802.11, 802.15.4, bluetooth. The catchall it seems. Dunno if NS has something of the kind in their pipeline.