Microsoft 365 features that help users manage their subscriptions, account settings, and billing information.
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You cannot directly downgrade from Microsoft 365 Personal to Microsoft 365 Basic because they are completely different plans and offer different benefits.
The Microsoft 365 Basic plan does not include premium desktop Office licenses. It only provides 100 GB of OneDrive (cloud) storage and 100 GB of Outlook email storage. So, you have correctly canceled your Microsoft 365 Personal subscription, which is the first step. And,
Yes, you will need to wait for your Microsoft 365 Personal subscription to expire before you can move to Microsoft 365 Basic. During this time (up to 30 days Max for renewal/switch plan), you will lose access to the Office desktop apps, and your files will be only available in read-only mode, but they will become accessible again once you subscribe to Microsoft 365 Basic.