Things seem to be on their way up now, and https://status.denic.de/ is working again, at least from here.

DENIC's status page currently says "Frankfurt am Main, 5 May 2026 – DENIC eG is currently experiencing a disruption in its DNS service for .de domains. As a result, all DNSSEC-signed .de domains are currently affected in their reachability. The root cause of the disruption has not yet been fully identified. DENIC’s technical teams are working intensively on analysis and on restoring stable operations as quickly as possible.