https://www.bleepingcomputer.com/news/microsoft/microsoft-edge-gets-tab-enhancements-and-improved-performance/

Microsoft Edge was redesigned with Chromium in January 2020 and it's getting better every month with new updates. Earlier this year, Microsoft announced that it's enabling support for sleeping tabs and now Microsoft is rolling out two new features - vertical tabs and startup boost.

Vertical tabs feature was first introduced last year and this feature has been designed to move the tabs bar from the top to the left side in a vertical layout and you can switch between old and new layout with one click.