The message pane containing favorites, folders, and conversations used to be able to collapse. This was incredibly helpful - especially in work from home setups - as it saved room on our screens. Currently, the message panel has a fixed minimum width.
Let's restore the collapsable message pane!
Our product teams have captured this feedback, and are planning adjustments on the 7/10 release (23.2.35 web) to address this. Thank you!
Update: These are now launched and fully rolled out, please make sure to restart your apps to see the latest version. If you have additional feedback after trying the latest updates that make the left panel sizing smaller width like the previous desktop app interface - let us know!