Hello, this is Emily.
From the sound of it, you have a paid Microsoft 365 package, right? If so, the classic Outlook is part of the 365 package, so you cannot simply just uninstall the classic Outlook. However, if you do have the paid Msft 365 package, you might want to switch OFF the "try new outlook" on the upper right to go back to classic, because the paid version of Outlook has way more features than the new Outlook.
The new Outlook is a push to replace the old free Windows Mail, that comes with Windows. I am not sure why Microsoft gives the "try new Outlook" also for the paid Outlook app that's part of 365, because the paid version is way better than the free new Outlook.
So, once you turn that toggle off to go back to the classic Outlook, you might want to uninstall Outlook (new) instead.