I never tried Zigbee, but I did get Thread working on a -C6:
It's just a template really.. of a "Dimmer" because I got the new C8-Pro T hub. It works with a built-in Generic Matter Dimmer driver. I'm surprised it doesn't work with Zigbee. (Matter is on all my hubs, Thread on only one hub. Zigbee is on just one hub too.)