As @bertabcd1234 indicated, HomeKit Controller isn't compatible with the C-8.
However, if you run an instance of Home Assistant (HA) on your home network (in a VM or on dedicated hardware), ecobee thermostats can be paired to HA via HomeKit. And, there's a Hubitat integration that permits devices paired to HA to be imported into Hubitat. I used this approach for a long time before switching to the new HomeKit Controller in Hubitat.