The Smart Lock has to “test” (by trying to connect) if the remote access via Thread is possible. This can take 1-2 minutes. i.e. if the switch becomes disabled shortly after enabling it, this means that you router does not support NAT64 (yet).
No, that’s not what is said. Every hub that has Thread 1.4 will have to have it (there are no Thread 1.4 hubs out there yet). Others might have it, such as all Apple thread hubs (AppleTV, HomePod Mini) and the Google Nest WIFI Pro. If you use a Raspberry with HomeAssistant as hub, you can also enable it.
We’re currently updating the list of hubs which we know to support it. Please check back the link i posted above in a few weeks.