Thank you for providing feedback on the new Outlook on the web experience. This is our new Outlook and the ability to go back to the previous format is not available. I am a Support Engineer with Microsoft and apologize for the poor experience and any inconvenience that was caused.
We are aware of the missing folder issue and our Product Team is working on releasing a fix in the near future. Please understand that your data is not lost. We are working on recovering this data and restoring it to your account as quickly as we can. We appreciate your patience.
Also, if you need help to learn about the new features, here
is a url to a self-help FAQ article with links to more