How to challenge a German Last Will and Testament
German Probate Courts routinely issue a German Grant of Probate (Erbschein) to the applicant without any pro-active investigation into the question whether the testator did possess legal capacity or not.
In other words, if nobody comes forward to challenge the validity of the last will, the German court will issue the Erbschein even if the German testator had suffered from severe dementia at the time the last will was written.
In case you consider challenging a German will by entering a caveat (stop notice), or in case you are the probate applicant who believes that the will is valid but someone else disputes the validity of the will, you can find valuable information in the following posts by German experts on succession law, probate and estate administration:
https://www.crosschannellawyers.co.uk/disputed-wills-and-contentious-probate-in-germany/
https://www.crosschannellawyers.co.uk/inheritance-disputes-in-germany/