Hello !
Thank you for posting on MS Learn Q&A.
For this case, do not keep creating new identity validation requests. Once the same entity starts getting rejected automatically, the portal flow usually will not give you enough information to self fix it.
Since the company is a German GmbH, country eligibility should not be the issue for Public Trust because Artifact Signing Public Trust is currently available for organizations in the EU, among other regions.
https://learn.microsoft.com/en-us/azure/artifact-signing/faq
Only Microsoft can tell why the vetting failed or unblock an auto rejection loop so prepare the IDs and documents and stop resubmitting blindly and push for manual review through Azure Support.