@Pesala True. But that would imply that Vivaldi would have to be "always listening", which might be badly interpreted. (I trust Vivaldi. Dont get me wrong). Maybe a long press on the speed dial icon or smt ? Or, if that's even possible, bind it to google assistant.
There is a read aloud feature called Narrator built in to Windows, Ease of Access.
Unfortunately, instead of reading the selected text it narrates a whole lot of other stuff. Try the shortcut, Windows Key + Ctrl + Enter to see what the issues are.