cat /etc/crypto-policies/back-ends/opensshserver.config
...
Ciphers aes256-gcm@openssh.com,chacha20-poly1305@openssh.com,aes256-ctr,aes128-gcm@openssh.com,aes128-ctr
 ...

...
 private enum SshCipher {        DESEDE_CBC(24, 8, "des-ede3-cbc") {
            @Override
            BlockCipher createBlockCipher(byte[] key, byte[] iv, boolean encrypt) {
                return BlockCipherFactory.createCipher("3des-cbc", encrypt, key, iv);
            }
        },
        DES_CBC(8, 8, "des-cbc") {
            @Override
            BlockCipher createBlockCipher(byte[] key, byte[] iv, boolean encrypt) {
                DES des = new DES();
                des.init(encrypt, key);
                return new CBCMode(des, iv, encrypt);
            }
        },
        AES128_CBC(16, 16, "aes-128-cbc", "aes128-cbc") {
            @Override
            BlockCipher createBlockCipher(byte[] key, byte[] iv, boolean encrypt) {
                return BlockCipherFactory.createCipher("aes128-cbc", encrypt, key, iv);
            }
        },
        AES192_CBC(24, 16, "aes-192-cbc", "aes192-cbc") {
            @Override
            BlockCipher createBlockCipher(byte[] key, byte[] iv, boolean encrypt) {
                return BlockCipherFactory.createCipher("aes192-cbc", encrypt, key, iv);
            }
        },
        AES256_CBC(32, 16, "aes-256-cbc", "aes256-cbc") {
            @Override
            BlockCipher createBlockCipher(byte[] key, byte[] iv, boolean encrypt) {
                return BlockCipherFactory.createCipher("aes256-cbc", encrypt, key, iv);
            }
        },
        AES256_CTR(32, 16, "aes-256-ctr", "aes256-ctr") {
            @Override
            BlockCipher createBlockCipher(byte[] key, byte[] iv, boolean encrypt) {
                return BlockCipherFactory.createCipher("aes256-ctr", encrypt, key, iv);
            }
        };        private final String[] sshCipherNames;
        private final int keyLength;
        private final int blockSize;        SshCipher(int keyLength, int blockSize, String cipherName, String... cipherAliases) {
            this.keyLength = keyLength;
            this.blockSize = blockSize;
            String[] sshCipherNames = new String[1 + (null == cipherAliases ? 0 : cipherAliases.length)];
            sshCipherNames[0] = cipherName;
            if (null != cipherAliases) {
                System.arraycopy(cipherAliases, 0, sshCipherNames, 1, cipherAliases.length);
            }
            this.sshCipherNames = sshCipherNames;
        }        abstract BlockCipher createBlockCipher(byte[] key, byte[] iv, boolean encrypt);        public int getBlockSize() {
            return blockSize;
        }        public int getKeyLength() {
            return keyLength;
        }        public static SshCipher getInstance(String cipher) {
            for (SshCipher instance : values()) {
                for (String name : instance.sshCipherNames) {
                    if (name.equalsIgnoreCase(cipher)) {
                        return instance;
                    }
                }
            }
            throw new IllegalArgumentException("Unknown Cipher: " + cipher);
        }    }

... 

verificationStrategy=hudson.plugins.sshslaves.verifiers.NonVerifyingKeyVerificationStrategy, tcpNoDelay=true, trackCredentials=true}[03/16/25 09:47:38] [SSH] Opening SSH connection to jenkins-agent-1.shelltech.net:22.[03/16/25 09:47:38] [SSH] WARNING: SSH Host Keys are not being verified. Man-in-the-middle attacks may be possible against this connection.ERROR: SSH authentication failedjava.lang.IllegalArgumentException: Unknown Cipher: aes256-gcm@openssh.com	at PluginClassLoader for trilead-api//com.trilead.ssh2.signature.OpenSshCertificateDecoder$SshCipher.getInstance(OpenSshCertificateDecoder.java:213)	at PluginClassLoader for trilead-api//com.trilead.ssh2.signature.OpenSshCertificateDecoder.createKeyPair(OpenSshCertificateDecoder.java:77)	at PluginClassLoader for trilead-api//com.trilead.ssh2.crypto.PEMDecoder.decodeKeyPair(PEMDecoder.java:471)	at PluginClassLoader for trilead-api//com.trilead.ssh2.auth.AuthenticationManager.authenticatePublicKey(AuthenticationManager.java:303)	at PluginClassLoader for trilead-api//com.trilead.ssh2.Connection.authenticateWithPublicKey(Connection.java:474)	at PluginClassLoader for ssh-credentials//com.cloudbees.jenkins.plugins.sshcredentials.impl.TrileadSSHPublicKeyAuthenticator.doAuthenticate(TrileadSSHPublicKeyAuthenticator.java:110)	at PluginClassLoader for ssh-credentials//com.cloudbees.jenkins.plugins.sshcredentials.SSHAuthenticator.authenticate(SSHAuthenticator.java:431)	at PluginClassLoader for ssh-credentials//com.cloudbees.jenkins.plugins.sshcredentials.SSHAuthenticator.authenticate(SSHAuthenticator.java:468)	at PluginClassLoader for ssh-slaves//hudson.plugins.sshslaves.SSHLauncher.openConnection(SSHLauncher.java:875)	at PluginClassLoader for ssh-slaves//hudson.plugins.sshslaves.SSHLauncher.lambda$launch$0(SSHLauncher.java:440)	at java.base/java.util.concurrent.FutureTask.run(FutureTask.java:264)	at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1136)	at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:635)	at java.base/java.lang.Thread.run(Thread.java:840)[03/16/25 09:47:38] [SSH] Authentication failed.Authentication failed.[03/16/25 09:47:38] Launch failed - cleaning up connection[03/16/25 09:47:38] [SSH] Connection closed.