This is a DNSSEC test zone dual-signed with ML-DSA-44 (algorithm 18, per draft-westerbaan-dnssec-mldsa) and ECDSAP256SHA256 (algorithm 13).
Every validating resolver should be able to validate this zone: via alg 18 if it supports ML-DSA-44, via alg 13 otherwise.
Try: dig +dnssec dual.alg18.westerbaan.name A
Related test zones: only (signed with alg 18 only) and downgrade (DNSKEY/DS for alg 18 and 13, but alg 18 signatures deliberately missing).