@letmein3-0 Other Chromium-based browsers show the extension URL too for extensions, except when the extension uses chrome_url_overrides to override the start page where the URL is then cleared.
However, Opera purposely blocks chrome_url_overides so that extensions can't override the start page. New Tab Start Page just happens to use a redirect instead for Opera to work around Opera's. But, New Tab Start Page doesn't clear the URL in that case (if it's even allowed to).
Since Opera purposely blocks overriding of the start page, Opera isn't going to do anything about situations where the start page is overridden. So, in this case, your only hope is to ask the other of the extension to clear the address field in this specific case if possible.
Of course, it would be nice if Opera would just allow chrome_url_overrides. Then there wouldn't be a need for any workarounds. But, Opera won't do that.