I have no plans in downloading Atlas either, but I think your browsing isn't used for training unless you opt in.

> By default, we don’t use the content you browse to train our models. If you choose to opt-in this content, you can enable “include web browsing” in your data controls settings. Note, even if you opt into training, webpages that opt out of GPTBot, will not be trained on.

https://openai.com/index/introducing-chatgpt-atlas/