For zigbee dongles, take a look at the SLZB-06. I used a sonoff usb dongle at first (which was fine), but then switched to the slzb which works nicer and lets you run it independently from your home assistant machine over Ethernet (you can still use usb if you like though).

I have like 50 ikea zigbee lights running off mine (plus the same amount of other zigbee stuff) and it works super stable with zigbee2mqtt.

For me, it didn’t prompt the upgrade when I went to the firmware page, but it did prompt for it when I went into the matter settings page.

I think Switchbot does slow rollouts, but if it’s not available for you yet you can just send them a message in the feedback page of the app and they’ll probably be able push the upgrade to you (I’ve done this a couple of times for previous matter releases).

It’s not thread-based matter to the vacuum directly, but matter over wifi using their Hub 2 as a bridge, but I just tested and it works! The vacuum shows up as a binary OnOff plug, toggling it on starts a cleaning session, and off cancels the session and returns the unit to base.

I should note, I had to update my Hub 2 firmware to V2.0-1.2, which also adds the ability to swap out the temperature and humidity sensors to other devices for being a matter bridge, which is nice.