Despite overwhelming claims that you can revert to the classic Outlook, that is not true in all cases. I recently loaded Office 365. The version of Office under the covers is 16. My husband did the same a number of months ago and his version "under the covers" is 15. None of what anyone has suggested for accessing Classic Outlook has been successful because no other version of Outlook was loaded when I installed Office 365. There is no file menu, no toggle switch and no distinction app icon wise for New Outlook. It's just Outlook with the new icon but no "New" anywhere on the icon. I also searched for Outlook besides the one that came with 365 and there is nada. I posed this dilemma to Google and their AI came back with that Microsoft was pushing the newer version of Outlook and was not making the classic version available anymore.
With that being said, I did recently have an issue with Office on my PC and had to uninstall it prior to installing Office 365. I am wondering if the ability to revert is only available if a prior version of Office (Outlook) is detected. Either way I have no choice but to use what is there. I did waste a considerable amount of time trying desperately to get back to my beloved classic Outlook. If not having a prior version of Outlook installed meant you just got "new" Outlook, it would be helpful if that information was available in an internet search.
I hope this post helps others who may find themselves in a similar situation.