The first link you referenced is for removing Google Nest devices (e.g., thermostats, locks, cameras, doorbells) from the Google Home app. It is not about removing a Wifi connected device from the Wifi device list in your Google Home app, although I totally get the potential confusion there.
Unfortunately, as per the second link you included, there is currently no way to manually edit or delete devices from the device list.
For you, is deleting them more about cleaning up the list, or preventing them from joining your Wifi again?
Cleaning up the list I get, I want it to be "clean" as well. Thought I'd ask the second question as that's actually not possible. Assuming it were possible to edit or delete devices in the list, all it would do is stop storing that information. There would be nothing to stop the device from joining your Wifi again as it already has the password. You would need to change your Wifi password to prevent that, and that's not a challenge unique to Nest Wifi.
We haven't heard from you in a while so we'll be locking this thread if there is no update within 24 hours. If you have any new issues, updates or just a discussion topic, feel free to start a new thread in the Community.