I think Google has actually removed all third-party integrations for Assistant a while ago: https://developers.google.com/assistant/ca-sunset

In other words, they have just closed down that entire ecosystem. I don't think there's an antitrust angle here: Forcing e.g. Apple to allow third-party apps or app stores seems within reach (at least in the EU); this would be more like forcing Apple to enable apps in a world where they don't even exist (anymore).

"If there is no banner, your Actions project is not a Conversational Action and won’t be affected."

Here, "conversational" means your voice command should prompt the app to ask you a question, driving a state machine. (Set a reminder. When do you want to be reminded?)

I haven't tried to use it, but the docs indicate CRUD-over-voice ("built-in intents") is unaffected.

https://developers.google.com/assistant/ca-sunset#what_will_...

https://developer.android.com/reference/app-actions/built-in...

Aren’t these only available on Android, though (i.e. not on Home speakers)?