Try the phone app.
This link tells you about it and at the bottom of the page how to disable. I think amazon would be in some deep 💩 if they sold devices that forced people to share internet without telling you. For one, it violates the contract agreement, and perhaps could be considered theft and fraud, a major class action suit with no luck of amazon winning.
If you read about sidewalk, the people who designed it and have made claims about it’s purported purpose are obviously city people. For example, if your power goes out, you could still have services from neighboring wi-fi. If my electricity is out, then the whole damn town is out, and there is no internet.
from your link:
Fortunately, turning Sidewalk off is relatively painless. It involves:
Opening the Alexa app
Opening More and selecting Settings
Selecting Account Settings
Selecting Amazon Sidewalk
Turning Amazon Sidewalk Off
It does say how to disable it, but at least, on my iPhone there is no sidewalk in the account settings to disable.