I'm the author of the article. This was added by Substack without my knowledge (it doesn't show up to me since I'm already subscribed) and I think I've disabled it now. Please check to confirm that it is disabled.
This is not disabled. I loaded the page a few minutes ago and it gave me the fullscreen popover. It appears about halfway down the page. I just re-loaded to check and there was no popover. When I load the page in a private browser session I still get the popover. So there appears to be a cookie that remembers the dismissal.
e: I cleared the substack cookies and my main browser session still doesn't get the popover but private sessions do.
This is not disabled. I loaded the page a few minutes ago and it gave me the fullscreen popover. It appears about halfway down the page. I just re-loaded to check and there was no popover. When I load the page in a private browser session I still get the popover. So there appears to be a cookie that remembers the dismissal.
e: I cleared the substack cookies and my main browser session still doesn't get the popover but private sessions do.