outdated documentation, there is no option to "register device model" in the console anymore
documentation at https://developers.google.com/assistant/sdk/guides/service/python/embed/register-device
says:
Use the registration UI Use the registration UI in the Actions Console to register a device model. Click the REGISTER MODEL button.

but actual console doesn't have this option

When you create a project, did you select the Device Registration option at the bottom of the onboarding page?
No, the instructions do not mention I should do it.
https://console.actions.google.com/project/your-project/deviceregistration/

this is really annoying, i spent 1 hour to find the register model button