DNSKEY flags only supports 0-255

DNSKEY record 256 is the public key called Zone-signing-key, used to verify the DNS record signatures for A, MX, CNAME, SRV, etc.
DNSKEY record 257 is called the Key-Signing Key, used to verify the signatures of the DNSKEY, CDS, and CDNSKEY records.

But cloudflare DNSKEY DNSKEY only supports 0-255.