Can I restore my whiteboard created by Microsoft Whiteboard UWP?

May refer on below:

Cloud storage requirement: Whiteboard content is automatically saved to the cloud only when you are signed in with a work or school account. Personal accounts now store boards in OneDrive for Business or SharePoint, depending on how your organization is set up.

Version history & recovery: Microsoft Whiteboard does not provide a local backup or version history for boards created in the old UWP app. Once the app updates and data is not synced to OneDrive/SharePoint, the boards are not recoverable.

The official documentation emphasizes that users should ensure boards are synced to OneDrive/Teams to avoid data loss. If boards are missing, the only supported path is to check your Whiteboard home page (web or app) and confirm whether they appear under your account. If not, may try contacting Microsoft Support directly, but recovery is not guaranteed.

https://github.com/MicrosoftDocs/microsoft-365-docs/blob/public/microsoft-365/whiteboard/manage-data-organizations.md

https://learn.microsoft.com/en-us/answers/questions/5643698/restore-lost-data-in-whiteboard