Way back in October 2020, Microsoft brought vertical tabs to Edge developer versions. The tabs are arranged on the left side of the screen rather than the top, in theory allowing more of the title to be visible.
So far however it has not been possible to resize the tabs and adjust just how much horizontal screen space you want to devote to tab titles.
In the latest Edge Canary Update, however (version 90.0.810.0) you can now easily adjust the width of the vertical tabs from icon-only to the full web page title.
Vertical tabs are currently only available in Edge Canary and Edge Dev. It is not known when Microsoft intends to roll it out more widely.
Thanks, Leo Varela for the tip.