Thanks for the notes here.
The Roku skill for Google Assistant is only currently available on Roku accounts/devices in the US at this time. If you are trying to access or use it in any other region, this would not be supported. We're always looking to expand our offerings and appreciate the interest here.
You can check our more about the Roku skill for Google Assistant here: https://support.roku.com/article/360009649613-how-do-i-use-the-google-assistant-with-my-roku-streami...
I would recommend removing the skill and your Roku device from your Google 'Home', restarting your device, then trying to add it back once more and see if this helps resolve the issue.
If you are using the Roku skill for Google Assistant with a Roku streaming player, this will not have the ability to turn off the TV that your Roku player is connected to. You can, however, use a voice command to turn Roku TVs on/off when the skill is enabled for those devices.