Ahhhh yea that’s likely why, Outlook is considered separate from O365 (stupid microsoft - O365 structure is SUPER convoluted).
O365 is traditionally the hosted Exchange plans far as I’ve seen. Though I THINK the Home/Personal O365 plans also work as O365? Not as sure on that part since those ones get branded Outlook instead of O365.
You can sign up for a free trial of the basic O365 plan via https://www.microsoft.com/en-us/microsoft-365/business/compare-all-microsoft-365-business-products otherwise if that’s too much trouble I may be able to help getcha a temporary O365 account for testing purposes 