Jenkins declarative pipeline ssh agent plugin

I'm trying to use sshagent plugin to deploy to remote server.

when using below syntax, I'm getting

pipeline {
    agent any
    stages {
        stage('Deploy') {
            steps {
                sshagent(['nginx-ec2']) {
                    // some block
                    sh "ssh -o StrictHostKeyChecking=no ubuntu@<host_ip>"
                    sh "whoami"
                }
            }
        }
    }
}

getting output:

[Pipeline] sh (hide)
+ whoami
jenkins

while I'm expecting to run script at the remote server using provided credentials !!

So, I had to run it this way

pipeline {
    agent any
    stages {
        stage('Deploy') {
            steps {
                sshagent(['nginx-ec2']) {
                    // some block
                    sh "ssh -o StrictHostKeyChecking=no -l ubuntu <host_ip> 'whoami && \
                    sudo apt update  && sudo apt install -y docker.io && \
                    sudo usermod -aG docker ubuntu && \
                    source .bashrc && \
                    docker run -d nginx'"
                }
            }
        }
    }
}

Is there any "clean" way to run script on remote server with ubuntu instead of jenkins user ?

Edit:

I understand I need to run it under the ssh command not as separate sh script otherwise, it will run as jenkins and I'm able to do it in the scripted way as below.

That's why I'm asking if there's a better way to write it in the declarative way.

node {
   stage('Deploy'){
     def dockerRun = "whoami && \
            sudo apt update  && sudo apt install -y docker.io && \
            sudo usermod -aG docker ubuntu && \
            source .bashrc && \
            docker run -d nginx "
            
     sshagent(['nginx-ec2']) {
       sh "ssh -o StrictHostKeyChecking=no ubuntu@<host_ip> '${dockerRun}' "
     }
   }
}

Thanks,