With old Presto Opera there was a valid stance of "it might not work and we are not going to test it". But with current Opera, or Vivaldi, and I'm sure many others, it should just work, since they are all Chromium based.

By the way, fun fact, old Opera had huge "compatibility" javascript where they fixed either general or specific issues that were result of developers not caring about the browser. Opera had over 50% share in certain markets at the time.