Since 99% of my use of Onedrive is by rclone I rarely login to the GUI. But I did today, and shown a link to Changes to Microsoft 365 email features and storage - Microsoft Support
Looks like they're trying to shrink the space that personal accounts have, by adding Outlook usage into the quota.
This feels a little like Amazon Cloud Drive; they went from unlimited down to a (relatively) expensive limited storage, and is now going away at the end of 2023 ( Amazon Drive is shutting down at the end of 2023 - The Verge ).
I wonder if more cloud providers are beginning to realise that storage is pretty expensive!