Anti-user website design
Well, in the past Firefox had a section in the settings where you could disable websites' ability to disable various parts of the UI. I'm not sure what would be the best thing to use with Vivaldi for this. There are probably many kinds of extensions available and some things could be achieved with a user CSS file. It would be neat to have some build-in options to prevent this crap. It harms accessibility too. Preventing popup windows is just a start.
@Gwen-Dragon, did you even read that post before moving it? It's a question about Vivaldi.
You could use uBlock Origin extension to disable 1st-party and 3rd-party scripts.
@kumiponi Sorry about my misinterpretation. I move back!