So, I have a disconnected Roku in my home app that's not mine. (Ex-gf). I've removed all family members, actually I redid the whole setup after moving. I've tried to unlink, it just keeps relinking and brings me back to home app. There's no remove device option in any of its menus. Doesn't affect anything, just annoys me a bit.
Thanks for reaching out.
Here's some steps on how to remove your device from the Home app:
When you remove a device from a home in the Google Home app:
You might also want to try removing your Roku account from your Google Account: https://goo.gle/3qmKl0u
Let us know how it goes.