I'm sorry to break it to you, but Vivaldi is built on the Chromium engine, which is the same engine used by Google Chrome. As a project it depends on Google which is not an EU company.

If you have to chose a fork from either Google or Mozilla, I'd say Mozilla is the least evil. I would suggest Mullvad browser as a better EU substitute. With either librewolf or Icecat as runners up (although not sure if EU based)

There is also ladybird which is a entirely new engine and not based on either Google or Mozilla's work. It is open source and non profit but I'm not sure if they are based in the EU.