The .DE Registry - Denic does not provide any grace period for domain expiration and also deletes the domain before expiry date (end of the month).
If the domain has expired and since it was not renewed in time it will be in Transit state at the .DE Registry.
To restore the .de domain, please contact the .DE Registry to transfer the domain back to your account.
Please check the below URLs for more details on this.
https://www.denic.de/en/service/transit-procedure
https://transit.secure.denic.de/en/