ECDSA server certificate signed by a ECDSA self-signed CA

out.txt

D:\TEMP>openssl pkcs12 -info -in aaa.pfx | openssl.exe x509 -noout -text
Enter Import Password:
MAC: sha1, Iteration 2000
MAC length: 20, salt length: 20
PKCS7 Encrypted data: pbeWithSHA1And3-KeyTripleDES-CBC, Iteration 2000
Certificate bag
Certificate:
    Data:
        Version: 3 (0x2)
        Serial Number: 123 (0x7b)
        Signature Algorithm: ecdsa-with-SHA256
        Issuer: CN = MyCA
        Validity
            Not Before: Oct 12 16:50:25 2021 GMT
            Not After : Jan 11 16:50:25 2022 GMT
        Subject: CN = MyServer
        Subject Public Key Info:
            Public Key Algorithm: id-ecPublicKey
                Public-Key: (256 bit)
                pub:
                    04:36:19:a5:f1:79:25:da:7d:dc:f5:42:34:ac:19:
                    f3:00:90:37:d2:dc:42:3c:80:c5:90:dc:cb:3b:95:
                    da:82:0b:d7:f8:7e:82:52:7e:22:c5:db:91:9b:bd:
                    50:6c:64:f9:cc:86:66:f9:c3:8f:76:5d:b7:fb:36:
                    51:ef:d6:56:4a
                ASN1 OID: prime256v1
                NIST CURVE: P-256
        X509v3 extensions:
            X509v3 Key Usage:
                Digital Signature, Data Encipherment
            X509v3 Subject Key Identifier:
                C1:83:41:4B:6F:C8:4A:06:43:E6:F4:46:8A:DA:EA:3C:FE:4A:E4:78
    Signature Algorithm: ecdsa-with-SHA256
         30:43:02:1f:09:0e:53:66:5d:de:ba:4d:57:aa:e1:75:8e:9c:
         86:48:4b:d5:b9:be:2e:f1:02:ff:4b:83:f4:ba:be:d6:ed:02:
         20:4d:16:92:67:20:39:6e:9d:d0:3c:fd:cf:ca:0e:3b:e8:5f:
         f4:dc:30:54:db:47:90:f4:04:a2:2b:67:21:57:13

Program.cs

using System;
using System.IO;
using System.Security.Cryptography;
using System.Security.Cryptography.X509Certificates;

namespace ConsoleApp1
{
    class Program
    {
        static void Main(string[] args)
        {
            using (var parent = ECDsa.Create(ECCurve.NamedCurves.nistP256))
            using (var srv = ECDsa.Create(ECCurve.NamedCurves.nistP256))
            {
                CertificateRequest parentReq = new CertificateRequest("CN=MyCA", parent, HashAlgorithmName.SHA256);

                parentReq.CertificateExtensions.Add(
                    new X509BasicConstraintsExtension(true, false, 0, true));

                parentReq.CertificateExtensions.Add(
                    new X509SubjectKeyIdentifierExtension(parentReq.PublicKey, false));

                using (X509Certificate2 parentCert = parentReq.CreateSelfSigned(
                    DateTimeOffset.UtcNow.AddDays(-45),
                    DateTimeOffset.UtcNow.AddDays(365)))
                {
                    CertificateRequest srvReq = new CertificateRequest(
                        "CN=MyServer",
                        srv,
                        HashAlgorithmName.SHA256);

                    srvReq.CertificateExtensions.Add(
                        new X509KeyUsageExtension(
                            X509KeyUsageFlags.DigitalSignature | X509KeyUsageFlags.DataEncipherment,
                            false));

                    srvReq.CertificateExtensions.Add(
                        new X509SubjectKeyIdentifierExtension(srvReq.PublicKey, false));

                    using (X509Certificate2 cert = srvReq.Create(
                        parentCert,
                        DateTimeOffset.UtcNow.AddDays(-1),
                        DateTimeOffset.UtcNow.AddDays(90),
                        new byte[] { 123 }))
                    {
                        File.WriteAllBytes(@"D:\TEMP\aaa.pfx", cert.Export(X509ContentType.Pfx));
                    }
                }
            }
        }
    }
}