@Pesala Good, I downgraded back to 6.5 and disabled updates, because I also experienced that 6.7 was stuck on loading tabs after Vivaldi was closed and opened again (I had to close it several times until it unstuck and started loading tabs and pages, Chrome and Firefox worked without any issue at that time) so it's not usable for me in this state...
BTW thanks to the tab grouping, possibility of opening new window or now with workspaces I never had so much tabs in the tab bar (I use it on the right side) which would lead to the hiding New tab bar...
However I still can't understand why there can't be two buttons (so have them in both positions) with possibility of hiding them in configuration?