What is your account type?
As far as I know, Teams Classic is about to expire, and you'll need to upgrade to save your previous data. Users may upgrade to either a fully featured Microsoft 365 subscription, or for a simpler and more affordable option, Microsoft Teams Essentials.
For more details, you could refer to: Upgrade from Microsoft Teams Free (classic) to Microsoft Teams.
If the answer is helpful, please click "Accept Answer" and kindly upvote it. If you have extra questions about this answer, please click "Comment".
Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.