At your own risk of any side effects, goto the URL opera://about, take note of the "install" path, close Opera and rename "opera_crashreporter.exe" in the latest version folder in the install folder to "opera_crashreporter.exe.off". Then, repeat after each time you update Opera.
If you're talking about the feedback smiley icon on the right, you can't remove it. You're not the only one to complain about it being present taking up a whole line on the page though.
It’s the same in regular Opera. You can’t change cookie settings at the moment. They will always return to default. That’s a bug, related to Chromium somehow but not appearing in Chrome or Vivaldi.