"expand tab bar on hoover" can not be checked, in settings the option is grey.
Linux Fedora 45 , Vivaldi 8.3.4191.30 (Official Build) (x86_64),
vivaldi browser NO expand tab bar on hoover
Submitted 19 hours ago by 
Jaapsoft@forum.vivaldi.net to vivaldi-for-linux@forum.vivaldi.net
https://forum.vivaldi.net/topic/122193/vivaldi-browser-no-expand-tab-bar-on-hoover
@Jaapsoft Only a point with tabs on sides. Please read:
https://help.vivaldi.com/desktop/tabs/tab-bar/
@Pathduck thanks a lot. This is the short answer,