As a German citizen, you are required to have an identity card from the age of 16 if you do not have a valid passport. Any theft of your identity card must be reported to the Bürgeramt or the police. If you do not do this, you are acting disorderly.
After reporting, you can apply for a new identity card. Provided you have a valid passport, you do not need to apply for a new ID card.
If you report the theft to your citizens' registration office or the police, the online ID card will be blocked as well.
You can also have the online ID card blocked yourself by telephone.

In order to prevent misuse, the card holder must immediately report the loss (loss, theft) of the ID card to the blocking hotline (116 116) or to the ID card authority for blocking of the online ID card function.

If you have also applied an electronic signature to the ID card, you must have the signature function blocked separately. In this regard, please contact the provider from whom you purchased the signature certificate and report the loss to them.

The blocking ensures that any attempted misuse is detected immediately. After the blocking, it is no longer possible to use the online ID card function of your ID card or to have it read out on site.
You can only have the signature function blocked by the provider of your signature certificate.

If you find the document again later, you must also report this.