<PackageReference Include="BouncyCastle.Cryptography" Version="2.7.0" />

Org.BouncyCastle.Crypto.Signers.Ed25519phSigner

public class Ed25519phSigner : ISigner
Ed25519ph (RFC 8032 ยง5.1) signature primitive: pre-hashes the message with SHA-512 before running pure Ed25519, parameterised by a fixed context captured at construction.
namespace Org.BouncyCastle.Crypto.Signers { public class Ed25519phSigner : ISigner { public virtual string AlgorithmName { get; } public Ed25519phSigner(byte[] context); public virtual void Init(bool forSigning, ICipherParameters parameters); public virtual void Update(byte b); public virtual void BlockUpdate(byte[] buf, int off, int len); public virtual void BlockUpdate(ReadOnlySpan<byte> input); public virtual int GetMaxSignatureSize(); public virtual byte[] GenerateSignature(); public virtual bool VerifySignature(byte[] signature); public void Reset(); } }